CHAPTER VI.

THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.

The secretion rendered acid by the direct and indirect excitement of
the glands—Nature of the acid—Digestible substances—Albumen, its
digestion arrested by alkalies, recommences by the addition of an
acid—Meat—Fibrin—Syntonin—Areolar tissue—Cartilage—Fibro-cartilage—
Bone—Enamel and dentine—Phosphate of lime—Fibrous basis of
bone—Gelatine—Chondrin— Milk, casein and
cheese—Gluten—Legumin—Pollen—Globulin—Haematin—Indigestible
substances—Epidermic productions—Fibro-elastic
tissue—Mucin—Pepsin—Urea—Chitine— Cellulose—Gun-cotton—Chlorophyll—Fat
and oil—Starch—Action of the secretion on living seeds—Summary and
concluding remarks.

As we have seen that nitrogenous fluids act very differently on the
leaves of Drosera from non-nitrogenous fluids, and as the leaves remain
clasped for a much longer time over various organic bodies than over
inorganic bodies, such as bits of glass, cinder, wood, &c., it becomes
an interesting inquiry, whether they can only absorb matter already in
solution, or render it soluble,—that is, have the power of digestion.
We shall immediately see that they certainly have this power, and that
they act on albuminous compounds in exactly the same manner as does the
gastric juice of mammals; the digested matter being afterwards
absorbed. This fact, which will be clearly proved, is a wonderful one
in the physiology of plants. I must here state that I have been aided
throughout all my later experiments by many valuable suggestions and
assistance given me with the greatest kindness by Dr. Burdon Sanderson.
[page 86]

It may be well to premise for the sake of any reader who knows nothing
about the digestion of albuminous compounds by animals that this is
effected by means of a ferment, pepsin, together with weak hydrochloric
acid, though almost any acid will serve. Yet neither pepsin nor an acid
by itself has any such power.* We have seen that when the glands of the
disc are excited by the contact of any object, especially of one
containing nitrogenous matter, the outer tentacles and often the blade
become inflected; the leaf being thus converted into a temporary cup or
stomach. At the same time the discal glands secrete more copiously, and
the secretion becomes acid. Moreover, they transmit some influence to
the glands of the exterior tentacles, causing them to pour forth a more
copious secretion, which also becomes acid or more acid than it was
before.

As this result is an important one, I will give the evidence. The
secretion of many glands on thirty leaves, which had not been in any
way excited, was tested with litmus paper; and the secretion of
twenty-two of these leaves did not in the least affect the colour,
whereas that of eight caused an exceedingly feeble and sometimes
doubtful tinge of red. Two other old leaves, however, which appeared to
have been inflected several times, acted much more decidedly on the
paper. Particles of clean glass were then placed on five of the leaves,
cubes of albumen on six, and bits of raw meat on three, on none of
which was the secretion at this time in the least acid. After an
interval of 24 hrs., when almost all the tentacles on

* It appears, however, according to Schiff, and contrary to the opinion
of some physiologists, that weak hydrochloric dissolves, though slowly,
a very minute quantity of coagulated albumen. Schiff, ‘Phys. de la
Digestion,’ tom. ii. 1867, p. 25. [page 87]

these fourteen leaves had become more or less inflected, I again tested
the secretion, selecting glands which had not as yet reached the centre
or touched any object, and it was now plainly acid. The degree of
acidity of the secretion varied somewhat on the glands of the same
leaf. On some leaves, a few tentacles did not, from some unknown cause,
become inflected, as often happens; and in five instances their
secretion was found not to be in the least acid; whilst the secretion
of the adjoining and inflected tentacles on the same leaf was decidedly
acid. With leaves excited by particles of glass placed on the central
glands, the secretion which collects on the disc beneath them was much
more strongly acid than that poured forth from the exterior tentacles,
which were as yet only moderately inflected. When bits of albumen (and
this is naturally alkaline), or bits of meat were placed on the disc,
the secretion collected beneath them was likewise strongly acid. As raw
meat moistened with water is slightly acid, I compared its action on
litmus paper before it was placed on the leaves, and afterwards when
bathed in the secretion; and there could not be the least doubt that
the latter was very much more acid. I have indeed tried hundreds of
times the state of the secretion on the discs of leaves which were
inflected over various objects, and never failed to find it acid. We
may, therefore, conclude that the secretion from unexcited leaves,
though extremely viscid, is not acid or only slightly so, but that it
becomes acid, or much more strongly so, after the tentacles have begun
to bend over any inorganic or organic object; and still more strongly
acid after the tentacles have remained for some time closely clasped
over any object.

I may here remind the reader that the secretion [page 88] appears to be
to a certain extent antiseptic, as it checks the appearance of mould
and infusoria, thus preventing for a time the discoloration and decay
of such substances as the white of an egg, cheese, &c. It therefore
acts like the gastric juice of the higher animals, which is known to
arrest putrefaction by destroying the microzymes.

[As I was anxious to learn what acid the secretion contained, 445
leaves were washed in distilled water, given me by Prof. Frankland; but
the secretion is so viscid that it is scarcely possible to scrape or
wash off the whole. The conditions were also unfavourable, as it was
late in the year and the leaves were small. Prof. Frankland with great
kindness undertook to test the fluid thus collected. The leaves were
excited by clean particles of glass placed on them 24 hrs. previously.
No doubt much more acid would have been secreted had the leaves been
excited by animal matter, but this would have rendered the analysis
more difficult. Prof. Frankland informs me that the fluid contained no
trace of hydrochloric, sulphuric, tartaric, oxalic, or formic acids.
This having been ascertained, the remainder of the fluid was evaporated
nearly to dryness, and acidified with sulphuric acid; it then evolved
volatile acid vapour, which was condensed and digested with carbonate
of silver. “The weight of the silver salt thus produced was only .37
gr., much too small a quantity for the accurate determination of the
molecular weight of the acid. The number obtained, however,
corresponded nearly with that of propionic acid; and I believe that
this, or a mixture of acetic and butyric acids, were present in the
liquid. The acid doubtless belongs to the acetic or fatty series.”

Prof. Frankland, as well as his assistant, observed (and this is an
important fact) that the fluid, “when acidified with sulphuric acid,
emitted a powerful odour like that of pepsin.” The leaves from which
the secretion had been washed were also sent to Prof. Frankland; they
were macerated for some hours, then acidified with sulphuric acid and
distilled, but no acid passed over. Therefore the acid which fresh
leaves contain, as shown by their discolouring litmus paper when
crushed, must be of a different nature from that present in the
secretion. Nor was any odour of pepsin emitted by them. [page 89]

Although it has long been known that pepsin with acetic acid has the
power of digesting albuminous compounds, it appeared advisable to
ascertain whether acetic acid could be replaced, without the loss of
digestive power, by the allied acids which are believed to occur in the
secretion of Drosera, namely, propionic, butyric, or valerianic. Dr.
Burdon Sanderson was so kind as to make for me the following
experiments, the results of which are valuable, independently of the
present inquiry. Prof. Frankland supplied the acids.

“1. The purpose of the following experiments was to determine the
digestive activity of liquids containing pepsin, when acidulated with
certain volatile acids belonging to the acetic series, in comparison
with liquids acidulated with hydrochloric acid, in proportion similar
to that in which it exists in gastric juice.

“2. It has been determined empirically that the best results are
obtained in artificial digestion when a liquid containing two per
thousand of hydrochloric acid gas by weight is used. This corresponds
to about 6.25 cubic centimetres per litre of ordinary strong
hydrochloric acid. The quantities of propionic, butyric, and valerianic
acids respectively which are required to neutralise as much base as
6.25 cubic centimetres of HCl, are in grammes 4.04 of propionic acid,
4.82 of butyric acid, and 5.68 of valerianic acid. It was therefore
judged expedient, in comparing the digestive powers of these acids with
that of hydrochloric acid, to use them in these proportions.

“3. Five hundred cub. cent. of a liquid containing about 8 cub. cent.
of a glycerine extract of the mucous membrane of the stomach of a dog
killed during digestion having been prepared, 10 cub. cent. of it were
evaporated and dried at 110o. This quantity yielded 0.0031 of residue.

“4. Of this liquid four quantities were taken which were severally
acidulated with hydrochloric, propionic, butyric, and valerianic acids,
in the proportions above indicated. Each liquid was then placed in a
tube, which was allowed to float in a water bath, containing a
thermometer which indicated a temperature of 38° to 40° Cent. Into
each, a quantity of unboiled fibrin was introduced, and the whole
allowed to stand for four hours, the temperature being maintained
during the whole time, and care being taken that each contained
throughout an excess of fibrin. At the end of the period each liquid
was filtered. Of the filtrate, which of course contained as much of the
fibrin as had been digested during the four hours, [page 90] 10 cub.
cent. were measured out and evaporated, and dried at 110° as before.
The residues were respectively—

“In the liquid containing hydrochloric acid 0.4079 ” ” propionic acid
0.0601 ” ” butyric acid 0.1468 ” ” valerianic acid 0.1254

“Hence, deducting from each of these the above-mentioned residue, left
when the digestive liquid itself was evaporated, viz. 0.0031, we have,

“For propionic acid 0.0570 ” butyric acid 0.1437 ” valerianic acid
0.1223

as compared with 0.4048 for hydrochloric acid; these several numbers
expressing the quantities of fibrin by weight digested in presence of
equivalent quantities of the respective acids under identical
conditions.

“The results of the experiment may be stated thus:—If 100 represent the
digestive power of a liquid containing pepsin with the usual proportion
of hydrochloric acid, 14.0, 35.4, and 30.2, will represent respectively
the digestive powers of the three acids under investigation.

“5. In a second experiment in which the procedure was in every respect
the same, excepting that all the tubes were plunged into the same
water-bath, and the residues dried at 115o C., the results were as
follows:—

“Quantity of fibrin dissolved in four hours by 10 cub. cent. of the
liquid:—

“Propionic acid 0.0563 Butyric acid 0.0835 Valerianic acid 0.0615

“The quantity digested by a similar liquid containing hydrochloric acid
was 0.3376. Hence, taking this as 100, the following numbers represent
the relative quantities digested by the other acids:—

“Propionic acid 16.5 Butyric acid 24.7 Valerianic acid 16.1

“6. A third experiment of the same kind gave: [page 91]

“Quantity of fibrin digested in four hours by 10 cub. cent. of the
liquid:—

“Hydrochloric acid 0.2915 Propionic acid 0.1490 Butyric acid 0.1044
Valerianic acid 0.0520

“Comparing, as before, the three last numbers with the first taken as
100, the digestive power of propionic acid is represented by 16.8; that
of butyric acid by 35.8; and that of valerianic by 17.8.

“The mean of these three sets of observations (hydrochloric acid being
taken as 100) gives for

“Propionic acid 15.8 Butyric acid 32.0 Valerianic acid 21.4

“7. A further experiment was made to ascertain whether the digestive
activity of butyric acid (which was selected as being apparently the
most efficacious) was relatively greater at ordinary temperatures than
at the temperature of the body. It was found that whereas 10 cub. cent.
of a liquid containing the ordinary proportion of hydrochloric acid
digested 0.1311 gramme, a similar liquid prepared with butyric acid
digested 0.0455 gramme of fibrin.

“Hence, taking the quantities digested with hydrochloric acid at the
temperature of the body as 100, we have the digestive power of
hydrochloric acid at the temperature of 16° to 18° Cent. represented by
44.9; that of butyric acid at the same temperature being 15.6.”

We here see that at the lower of these two temperatures, hydrochloric
acid with pepsin digests, within the same time, rather less than half
the quantity of fibrin compared with what it digests at the higher
temperature; and the power of butyric acid is reduced in the same
proportion under similar conditions and temperatures. We have also seen
that butyric acid, which is much more efficacious than propionic or
valerianic acids, digests with pepsin at the higher temperature less
than a third of the fibrin which is digested at the same temperature by
hydrochloric acid.] [page 92]

I will now give in detail my experiments on the digestive power of the
secretion of Drosera, dividing the substances tried into two series,
namely those which are digested more or less completely, and those
which are not digested. We shall presently see that all these
substances are acted on by the gastric juice of the higher animals in
the same manner. I beg leave to call attention to the experiments under
the head albumen, showing that the secretion loses its power when
neutralised by an alkali, and recovers it when an acid is added.

Substances which are completely or partially digested by the Secretion
of Drosera.

Albumen.—After having tried various substances, Dr. Burdon Sanderson
suggested to me the use of cubes of coagulated albumen or hard-boiled
egg. I may premise that five cubes of the same size as those used in
the following experiments were placed for the sake of comparison at the
same time on wet moss close to the plants of Drosera. The weather was
hot, and after four days some of the cubes were discoloured and mouldy,
with their angles a little rounded; but they were not surrounded by a
zone of transparent fluid as in the case of those undergoing digestion.
Other cubes retained their angles and white colour. After eight days
all were somewhat reduced in size, discoloured, with their angles much
rounded. Nevertheless in four out of the five specimens, the central
parts were still white and opaque. So that their state differed widely,
as we shall see, from that of the cubes subjected to the action of the
secretion.

Rather large cubes of albumen were first tried; the tentacles were well
inflected in 24 hrs.; after an [page 93] additional day the angles of
the cubes were dissolved and rounded;* but the cubes were too large, so
that the leaves were injured, and after seven days one died and the
others were dying. Albumen which has been kept for four or five days,
and which, it may be presumed, has begun to decay slightly, seems to
act more quickly than freshly boiled eggs. As the latter were generally
used, I often moistened them with a little saliva, to make the
tentacles close more quickly.

Experiment 2.—A cube of 1/10 of an inch (i.e. with each side 1/10 of an
inch, or 2.54 mm. in length) was placed on a leaf, and after 50 hrs. it
was converted into a sphere about 3/40 of an inch (1.905 mm.) in
diameter, surrounded by perfectly transparent fluid. After ten days the
leaf re-expanded, but there was still left on the disc a minute bit of
albumen now rendered transparent. More albumen had been given to this
leaf than could be dissolved or digested.

Experiment 3.—Two cubes of albumen of 1/20 of an inch (1.27 mm.) were
placed on two leaves. After 46 hrs. every atom of one was dissolved,
and most of the liquefied matter was absorbed, the fluid which remained
being in this, as in all other cases, very acid and viscid. The other
cube was acted on at a rather slower rate.

Experiment 4.—Two cubes of albumen of the same size as the last were
placed on two leaves, and were converted in 50 hrs. into two large
drops of transparent fluid; but when these were removed from beneath
the inflected tentacles, and viewed by reflected light under the
microscope, fine streaks of white opaque matter could be seen in the
one, and traces of similar streaks in the other. The drops were
replaced on the leaves, which re-expanded after 10 days; and now
nothing was left except a very little transparent acid fluid.

Experiment 5.—This experiment was slightly varied, so that the albumen
might be more quickly exposed to the action of the secretion. Two
cubes, each of about 1/40 of an inch (.635 mm.), were placed on the
same leaf, and two similar cubes on another

* In all my numerous experiments on the digestion of cubes of albumen,
the angles and edges were invariably first rounded. Now, Schiff states
(‘Leçons phys. de la Digestion,’ vol. ii. 1867, page 149) that this is
characteristic of the digestion of albumen by the gastric juice of
animals. On the other hand, he remarks “les dissolutions, en chimie,
ont lieu sur toute la surface des corps en contact avec l’agent
dissolvant.” [page 94]

leaf. These were examined after 21 hrs. 30 m., and all four were found
rounded. After 46 hrs. the two cubes on the one leaf were completely
liquefied, the fluid being perfectly transparent; on the other leaf
some opaque white streaks could still be seen in the midst of the
fluid. After 72 hrs. these streaks disappeared, but there was still a
little viscid fluid left on the disc; whereas it was almost all
absorbed on the first leaf. Both leaves were now beginning to
re-expand.]

The best and almost sole test of the presence of some ferment analogous
to pepsin in the secretion appeared to be to neutralise the acid of the
secretion with an alkali, and to observe whether the process of
digestion ceased; and then to add a little acid and observe whether the
process recommenced. This was done, and, as we shall see, with success,
but it was necessary first to try two control experiments; namely,
whether the addition of minute drops of water of the same size as those
of the dissolved alkalies to be used would stop the process of
digestion; and, secondly, whether minute drops of weak hydrochloric
acid, of the same strength and size as those to be used, would injure
the leaves. The two following experiments were therefore tried:—

Experiment 6.—Small cubes of albumen were put on three leaves, and
minute drops of distilled water on the head of a pin were added two or
three times daily. These did not in the least delay the process; for,
after 48 hrs., the cubes were completely dissolved on all three leaves.
On the third day the leaves began to re-expand, and on the fourth day
all the fluid was absorbed.

Experiment 7.—Small cubes of albumen were put on two leaves, and minute
drops of hydrochloric acid, of the strength of one part to 437 of
water, were added two or three times. This did not in the least delay,
but seemed rather to hasten, the process of digestion; for every trace
of the albumen disappeared in 24 hrs. 30 m. After three days the leaves
partially re-expanded, and by this time almost all the viscid fluid on
their discs was absorbed. It is almost superfluous to state that [page
95] cubes of albumen of the same size as those above used, left for
seven days in a little hydrochloric acid of the above strength,
retained all their angles as perfect as ever.

Experiment 8.—Cubes of albumen (of 1/20 of an inch, or 2.54 mm.) were
placed on five leaves, and minute drops of a solution of one part of
carbonate of soda to 437 of water were added at intervals to three of
them, and drops of carbonate of potash of the same strength to the
other two. The drops were given on the head of a rather large pin, and
I ascertained that each was equal to about 1/10 of a minim (.0059 ml.),
so that each contained only 1/4800 of a grain (.0135 mg.) of the
alkali. This was not sufficient, for after 46 hrs. all five cubes were
dissolved.

Experiment 9.—The last experiment was repeated on four leaves, with
this difference, that drops of the same solution of carbonate of soda
were added rather oftener, as often as the secretion became acid, so
that it was much more effectually neutralised. And now after 24 hrs.
the angles of three of the cubes were not in the least rounded, those
of the fourth being so in a very slight degree. Drops of extremely weak
hydrochloric acid (viz. one part to 847 of water) were then added, just
enough to neutralise the alkali which was still present; and now
digestion immediately recommenced, so that after 23 hrs. 30 m. three of
the cubes were completely dissolved, whilst the fourth was converted
into a minute sphere, surrounded by transparent fluid; and this sphere
next day disappeared.

Experiment 10.—Stronger solutions of carbonate of soda and of potash
were next used, viz. one part to 109 of water; and as the same-sized
drops were given as before, each drop contained 1/1200 of a grain
(.0539 mg.) of either salt. Two cubes of albumen (each about 1/40 of an
inch, or .635 mm.) were placed on the same leaf, and two on another.
Each leaf received, as soon as the secretion became slightly acid (and
this occurred four times within 24 hrs.), drops either of the soda or
potash, and the acid was thus effectually neutralised. The experiment
now succeeded perfectly, for after 22 hrs. the angles of the cubes were
as sharp as they were at first, and we know from experiment 5 that such
small cubes would have been completely rounded within this time by the
secretion in its natural state. Some of the fluid was now removed with
blotting-paper from the discs of the leaves, and minute drops of
hydrochloric acid of the strength of the one part to 200 of water was
added. Acid of this greater strength was used as the solutions of the
alkalies were stronger. The [page 96] process of digestion now
commenced, so that within 48 hrs. from the time when the acid was given
the four cubes were not only completely dissolved, but much of the
liquefied albumen was absorbed.

Experiment 11.—Two cubes of albumen (1/40 of an inch, or .635 mm.) were
placed on two leaves, and were treated with alkalies as in the last
experiment, and with the same result; for after 22 hrs. they had their
angles perfectly sharp, showing that the digestive process had been
completely arrested. I then wished to ascertain what would be the
effect of using stronger hydrochloric acid; so I added minute drops of
the strength of 1 per cent. This proved rather too strong, for after 48
hrs. from the time when the acid was added one cube was still almost
perfect, and the other only very slightly rounded, and both were
stained slightly pink. This latter fact shows that the leaves were
injured,* for during the normal process of digestion the albumen is not
thus coloured, and we can thus understand why the cubes were not
dissolved.]

From these experiments we clearly see that the secretion has the power
of dissolving albumen, and we further see that if an alkali is added,
the process of digestion is stopped, but immediately recommences as
soon as the alkali is neutralised by weak hydrochloric acid. Even if I
had tried no other experiments than these, they would have almost
sufficed to prove that the glands of Drosera secrete some ferment
analogous to pepsin, which in presence of an acid gives to the
secretion its power of dissolving albuminous compounds.

Splinters of clean glass were scattered on a large number of leaves,
and these became moderately inflected. They were cut off and divided
into three lots; two of them, after being left for some time in a
little distilled water, were strained, and some dis-

* Sachs remarks (‘Traité de Bot.’ 1874, p. 774), that cells which are
killed by freezing, by too great heat, or by chemical agents, allow all
their colouring matter to escape into the surrounding water. [page 97]

coloured, viscid, slightly acid fluid was thus obtained. The third lot
was well soaked in a few drops of glycerine, which is well known to
dissolve pepsin. Cubes of albumen (1/20 of an inch) were now placed in
the three fluids in watch-glasses, some of which were kept for several
days at about 90° Fahr. (32°.2 Cent.), and others at the temperature of
my room; but none of the cubes were dissolved, the angles remaining as
sharp as ever. This fact probably indicates that the ferment is not
secreted until the glands are excited by the absorption of a minute
quantity of already soluble animal matter,—a conclusion which is
supported by what we shall hereafter see with respect to Dionaea. Dr.
Hooker likewise found that, although the fluid within the pitchers of
Nepenthes possesses extraordinary power of digestion, yet when removed
from the pitchers before they have been excited and placed in a vessel,
it has no such power, although it is already acid; and we can account
for this fact only on the supposition that the proper ferment is not
secreted until some exciting matter is absorbed.

On three other occasions eight leaves were strongly excited with
albumen moistened with saliva; they were then cut off, and allowed to
soak for several hours or for a whole day in a few drops of glycerine.
Some of this extract was added to a little hydrochloric acid of various
strengths (generally one to 400 of water), and minute cubes of albumen
were placed in the mixture.* In two of these trials the cubes were not
in the least acted on; but in the third

* As a control experiment bits of albumen were placed in the same
glycerine with hydrochloric acid of the same strength; and the albumen,
as might have been expected, was not in the least affected after two
days. [page 98]

the experiment was successful. For in a vessel containing two cubes,
both were reduced in size in 3 hrs.; and after 24 hrs. mere streaks of
undissolved albumen were left. In a second vessel, containing two
minute ragged bits of albumen, both were likewise reduced in size in 3
hrs., and after 24 hrs. completely disappeared. I then added a little
weak hydrochloric acid to both vessels, and placed fresh cubes of
albumen in them; but these were not acted on. This latter fact is
intelligible according to the high authority of Schiff,* who has
demonstrated, as he believes, in opposition to the view held by some
physiologists, that a certain small amount of pepsin is destroyed
during the act of digestion. So that if my solution contained, as is
probable, an extremely small amount of the ferment, this would have
been consumed by the dissolution of the cubes of albumen first given;
none being left when the hydrochloric acid was added. The destruction
of the ferment during the process of digestion, or its absorption after
the albumen had been converted into a peptone, will also account for
only one out of the three latter sets of experiments having been
successful.

Digestion of Roast Meat.—Cubes of about 1/20 of an inch (1.27 mm.) of
moderately roasted meat were placed on five leaves which became in 12
hrs. closely inflected. After 48 hrs. I gently opened one leaf, and the
meat now consisted of a minute central sphere, partially digested and
surrounded by a thick envelope of transparent viscid fluid. The whole,
without being much disturbed, was removed and placed under the
microscope. In the central part the transverse striae on the muscular
fibres were quite distinct; and it was

* ‘Leçons phys. de la Digestion,’ 1867, tom. ii. pp. 114-126. [page 99]

interesting to observe how gradually they disappeared, when the same
fibre was traced into the surrounding fluid. They disappeared by the
striae being replaced by transverse lines formed of excessively minute
dark points, which towards the exterior could be seen only under a very
high power; and ultimately these points were lost. When I made these
observations, I had not read Schiff’s account* of the digestion of meat
by gastric juice, and I did not understand the meaning of the dark
points. But this is explained in the following statement, and we
further see how closely similar is the process of digestion by gastric
juice and by the secretion of Drosera.

“On a dit le suc gastrique faisait perdre à la fibre musculaire ses
stries transversales. Ainsi énoncée, cette proposition pourrait donner
lieu à une équivoque, car ce qui se perd, ce n’est que _l’aspect_
extérieur de la striature et non les éléments anatomiques qui la
composent. On sait que les stries qui donnent un aspect si
caractéristique à la fibre musculaire, sont le résultat de la
juxtaposition et du parallélisme des corpuscules élémentaires, placés,
à distances égales, dans l’intérieur des fibrilles contiguës. Or, dès
que le tissu connectif qui relie entre elles les fibrilles élémentaires
vient à se gonfler et à se dissoudre, et que les fibrilles elles-mêmes
se dissocient, ce parallélisme est détruit et avec lui l’aspect, le
phénomène optique des stries. Si, après la désagrégation des fibres, on
examine au microscope les fibrilles élémentaires, on distingue encore
très-nettement à leur intérieur les corpuscules, et on continue à les
voir, de plus en plus pâles, jusqu’au moment où les fibrilles
elles-mêmes se liquéfient et disparaissent dans le suc gastrique. Ce
qui constitue la striature, à proprement parler, n’est donc pas
détruit, avant la liquéfaction de la fibre charnue elle-même.”

In the viscid fluid surrounding the central sphere of undigested meat
there were globules of fat and little bits of fibro-elastic tissue;
neither of which were in

* ‘Leçons phys. de la Digestion,’ tom. ii. p. 145. [page 100]

the least digested. There were also little free parallelograms of
yellowish, highly translucent matter. Schiff, in speaking of the
digestion of meat by gastric juice, alludes to such parallelograms, and
says:—

“Le gonflement par lequel commence la digestion de la viande, résulte
de l’action du suc gastrique acide sur le tissu connectif qui se
dissout d’abord, et qui, par sa liquéfaction, désagrége les fibrilles.
Celles-ci se dissolvent ensuite en grande partie, mais, avant de passer
à l’état liquide, elles tendent à se briser en petits fragments
transversaux. Les ‘_sarcous elements_’ de Bowman, qui ne sont autre
chose que les produits de cette division transversale des fibrilles
élémentaires, peuvent être préparés et isolés à l’aide du suc
gastrique, pourvu qu’on n’attend pas jusqu’à la liquéfaction complète
du muscle.”

After an interval of 72 hrs., from the time when the five cubes were
placed on the leaves, I opened the four remaining ones. On two nothing
could be seen but little masses of transparent viscid fluid; but when
these were examined under a high power, fat-globules, bits of
fibro-elastic tissue, and some few parallelograms of sarcous matter,
could be distinguished, but not a vestige of transverse striae. On the
other two leaves there were minute spheres of only partially digested
meat in the centre of much transparent fluid.

Fibrin.—Bits of fibrin were left in water during four days, whilst the
following experiments were tried, but they were not in the least acted
on. The fibrin which I first used was not pure, and included dark
particles: it had either not been well prepared or had subsequently
undergone some change. Thin portions, about 1/10 of an inch square,
were placed on several leaves, and though the fibrin was soon
liquefied, the whole was never dissolved. Smaller particles were then
placed on four leaves, and minute [page 101] drops of hydrochloric acid
(one part to 437 of water) were added; this seemed to hasten the
process of digestion, for on one leaf all was liquified and absorbed
after 20 hrs.; but on the three other leaves some undissolved residue
was left after 48 hrs. It is remarkable that in all the above and
following experiments, as well as when much larger bits of fibrin were
used, the leaves were very little excited; and it was sometimes
necessary to add a little saliva to induce complete inflection. The
leaves, moreover, began to re-expand after only 48 hrs., whereas they
would have remained inflected for a much longer time had insects, meat,
cartilage, albumen, &c., been placed on them.

I then tried some pure white fibrin, sent me by Dr. Burdon Sanderson.

[Experiment 1.—Two particles, barely 1/20 of an inch (1.27 mm.) square,
were placed on opposite sides of the same leaf. One of these did not
excite the surrounding tentacles, and the gland on which it rested soon
dried. The other particle caused a few of the short adjoining tentacles
to be inflected, the more distant ones not being affected. After 24
hrs. both were almost, and after 72 hrs. completely, dissolved.

Experiment 2.—The same experiment with the same result, only one of the
two bits of fibrin exciting the short surrounding tentacles. This bit
was so slowly acted on that after a day I pushed it on to some fresh
glands. In three days from the time when it was first placed on the
leaf it was completely dissolved.

Experiment 3.—Bits of fibrin of about the same size as before were
placed on the discs of two leaves; these caused very little inflection
in 23 hrs., but after 48 hrs. both were well clasped by the surrounding
short tentacles, and after an additional 24 hrs. were completely
dissolved. On the disc of one of these leaves much clear acid fluid was
left.

Experiment 4.—Similar bits of fibrin were placed on the discs of two
leaves; as after 2 hrs. the glands seemed rather dry, they were freely
moistened with saliva; this soon caused strong inflection both of the
tentacles and blades, with copious [page 102] secretion from the
glands. In 18 hrs. the fibrin was completely liquefied, but undigested
atoms still floated in the liquid; these, however, disappeared in under
two additional days.]

From these experiments it is clear that the secretion completely
dissolves pure fibrin. The rate of dissolution is rather slow; but this
depends merely on this substance not exciting the leaves sufficiently,
so that only the immediately adjoining tentacles are inflected, and the
supply of secretion is small.

Syntonin.—This substance, extracted from muscle, was kindly prepared
for me by Dr. Moore. Very differently from fibrin, it acts quickly and
energetically. Small portions placed on the discs of three leaves
caused their tentacles and blades to be strongly inflected within 8
hrs.; but no further observations were made. It is probably due to the
presence of this substance that raw meat is too powerful a stimulant,
often injuring or even killing the leaves.

Areolar Tissue.—Small portions of this tissue from a sheep were placed
on the discs of three leaves; these became moderately well inflected in
24 hrs., but began to re-expand after 48 hrs., and were fully
re-expanded in 72 hrs., always reckoning from the time when the bits
were first given. This substance, therefore, like fibrin, excites the
leaves for only a short time. The residue left on the leaves, after
they were fully re-expanded, was examined under a high power and found
much altered, but, owing to the presence of a quantity of elastic
tissue, which is never acted on, could hardly be said to be in a
liquefied condition.

Some areolar tissue free from elastic tissue was next procured from the
visceral cavity of a toad, and moderately sized, as well as very small,
bits were placed on five leaves. After 24 hrs. two of the bits [page
103] were completely liquefied; two others were rendered transparent,
but not quite liquefied; whilst the fifth was but little affected.
Several glands on the three latter leaves were now moistened with a
little saliva, which soon caused much inflection and secretion, with
the result that in the course of 12 additional hrs. one leaf alone
showed a remnant of undigested tissue. On the discs of the four other
leaves (to one of which a rather large bit had been given) nothing was
left except some transparent viscid fluid. I may add that some of this
tissue included points of black pigment, and these were not at all
affected. As a control experiment, small portions of this tissue were
left in water and on wet moss for the same length of time, and remained
white and opaque. From these facts it is clear that areolar tissue is
easily and quickly digested by the secretion; but that it does not
greatly excite the leaves.

Cartilage.—Three cubes (1/20 of an inch or 1.27 mm.) of white,
translucent, extremely tough cartilage were cut from the end of a
slightly roasted leg-bone of a sheep. These were placed on three
leaves, borne by poor, small plants in my greenhouse during November;
and it seemed in the highest degree improbable that so hard a substance
would be digested under such unfavourable circumstances. Nevertheless,
after 48 hrs., the cubes were largely dissolved and converted into
minute spheres, surrounded by transparent, very acid fluid. Two of
these spheres were completely softened to their centres; whilst the
third still contained a very small irregularly shaped core of solid
cartilage. Their surfaces were seen under the microscope to be
curiously marked by prominent ridges, showing that the cartilage had
been unequally corroded by the secretion. I need hardly [page 104] say
that cubes of the same cartilage, kept in water for the same length of
time, were not in the least affected.

During a more favourable season, moderately sized bits of the skinned
ear of a cat, which includes cartilage, areolar and elastic tissue,
were placed on three leaves. Some of the glands were touched with
saliva, which caused prompt inflection. Two of the leaves began to
re-expand after three days, and the third on the fifth day. The fluid
residue left on their discs was now examined, and consisted in one case
of perfectly transparent, viscid matter; in the other two cases, it
contained some elastic tissue and apparently remnants of half digested
areolar tissue.

Fibro-cartilage (from between the vertebrae of the tail of a sheep).
Moderately sized and small bits (the latter about 1/20 of an inch) were
placed on nine leaves. Some of these were well and some very little
inflected. In the latter case the bits were dragged over the discs, so
that they were well bedaubed with the secretion, and many glands thus
irritated. All the leaves re-expanded after only two days; so that they
were but little excited by this substance. The bits were not liquefied,
but were certainly in an altered condition, being swollen, much more
transparent, and so tender as to disintegrate very easily. My son
Francis prepared some artificial gastric juice, which was proved
efficient by quickly dissolving fibrin, and suspended portions of the
fibro-cartilage in it. These swelled and became hyaline, exactly like
those exposed to the secretion of Drosera, but were not dissolved. This
result surprised me much, as two physiologists were of opinion that
fibro-cartilage would be easily digested by gastric juice. I therefore
asked Dr. Klein to examine the specimens; and [page 105] he reports
that the two which had been subjected to artificial gastric juice were
“in that state of digestion in which we find connective tissue when
treated with an acid, viz. swollen, more or less hyaline, the fibrillar
bundles having become homogeneous and lost their fibrillar structure.”
In the specimens which had been left on the leaves of Drosera, until
they re-expanded, “parts were altered, though only slightly so, in the
same manner as those subjected to the gastric juice as they had become
more transparent, almost hyaline, with the fibrillation of the bundles
indistinct.” Fibro-cartilage is therefore acted on in nearly the same
manner by gastric juice and by the secretion of Drosera.

Bone.—Small smooth bits of the dried hyoidal bone of a fowl moistened
with saliva were placed on two leaves, and a similarly moistened
splinter of an extremely hard, broiled mutton-chop bone on a third
leaf. These leaves soon became strongly inflected, and remained so for
an unusual length of time; namely, one leaf for ten and the other two
for nine days. The bits of bone were surrounded all the time by acid
secretion. When examined under a weak power, they were found quite
softened, so that they were readily penetrated by a blunt needle, torn
into fibres, or compressed. Dr. Klein was so kind as to make sections
of both bones and examine them. He informs me that both presented the
normal appearance of decalcified bone, with traces of the earthy salts
occasionally left. The corpuscles with their processes were very
distinct in most parts; but in some parts, especially near the
periphery of the hyoidal bone, none could be seen. Other parts again
appeared amorphous, with even the longitudinal striation of bone not
distinguishable. This amorphous structure, [page 106] as Dr. Klein
thinks, may be the result either of the incipient digestion of the
fibrous basis or of all the animal matter having been removed, the
corpuscles being thus rendered invisible. A hard, brittle, yellowish
substance occupied the position of the medulla in the fragments of the
hyoidal bone.

As the angles and little projections of the fibrous basis were not in
the least rounded or corroded, two of the bits were placed on fresh
leaves. These by the next morning were closely inflected, and remained
so,—the one for six and the other for seven days,—therefore for not so
long a time as on the first occasion, but for a much longer time than
ever occurs with leaves inflected over inorganic or even over many
organic bodies. The secretion during the whole time coloured litmus
paper of a bright red; but this may have been due to the presence of
the acid super-phosphate of lime. When the leaves re-expanded, the
angles and projections of the fibrous basis were as sharp as ever. I
therefore concluded, falsely as we shall presently see, that the
secretion cannot touch the fibrous basis of bone. The more probable
explanation is that the acid was all consumed in decomposing the
phosphate of lime which still remained; so that none was left in a free
state to act in conjunction with the ferment on the fibrous basis.

Enamel and Dentine.—As the secretion decalcified ordinary bone, I
determined to try whether it would act on enamel and dentine, but did
not expect that it would succeed with so hard a substance as enamel.
Dr. Klein gave me some thin transverse slices of the canine tooth of a
dog; small angular fragments of which were placed on four leaves; and
these were examined each succeeding day at the same hour. The results
are, I think, worth giving in detail.] [page 107]

[Experiment 1.—May 1st, fragment placed on leaf; 3rd, tentacles but
little inflected, so a little saliva was added; 6th, as the tentacles
were not strongly inflected, the fragment was transferred to another
leaf, which acted at first slowly, but by the 9th closely embraced it.
On the 11th this second leaf began to re-expand; the fragment was
manifestly softened, and Dr. Klein reports, “a great deal of enamel and
the greater part of the dentine decalcified.”

Experiment 2.—May 1st, fragment placed on leaf; 2nd, tentacles fairly
well inflected, with much secretion on the disc, and remained so until
the 7th, when the leaf re-expanded. The fragment was now transferred to
a fresh leaf, which next day (8th) was inflected in the strongest
manner, and thus remained until the 11th, when it re-expanded. Dr.
Klein reports, “a great deal of enamel and the greater part of the
dentine decalcified.”

Experiment 3.—May 1st, fragment moistened with saliva and placed on a
leaf, which remained well inflected until 5th, when it re-expanded. The
enamel was not at all, and the dentine only slightly, softened. The
fragment was now transferred to a fresh leaf, which next morning (6th)
was strongly inflected, and remained so until the 11th. The enamel and
dentine both now somewhat softened; and Dr. Klein reports, “less than
half the enamel, but the greater part of the dentine decalcified.”

Experiment 4.—May 1st, a minute and thin bit of dentine, moistened with
saliva, was placed on a leaf, which was soon inflected, and re-expanded
on the 5th. The dentine had become as flexible as thin paper. It was
then transferred to a fresh leaf, which next morning (6th) was strongly
inflected, and reopened on the 10th. The decalcified dentine was now so
tender that it was torn into shreds merely by the force of the
re-expanding tentacles.]

From these experiments it appears that enamel is attacked by the
secretion with more difficulty than dentine, as might have been
expected from its extreme hardness; and both with more difficulty than
ordinary bone. After the process of dissolution has once commenced, it
is carried on with greater ease; this may be inferred from the leaves,
to which the fragments were transferred, becoming in all four cases
strongly inflected in the course of a single day; whereas the first set
of leaves acted much less quickly and [page 108] energetically. The
angles or projections of the fibrous basis of the enamel and dentine
(except, perhaps, in No. 4, which could not be well observed) were not
in the least rounded; and Dr. Klein remarks that their microscopical
structure was not altered. But this could not have been expected, as
the decalcification was not complete in the three specimens which were
carefully examined.

Fibrous Basis of Bone.—I at first concluded, as already stated, that
the secretion could not digest this substance. I therefore asked Dr.
Burdon Sanderson to try bone, enamel, and dentine, in artificial
gastric juice, and he found that they were after a considerable time
completely dissolved. Dr. Klein examined some of the small lamellae,
into which part of the skull of a cat became broken up after about a
week’s immersion in the fluid, and he found that towards the edges the
“matrix appeared rarefied, thus producing the appearance as if the
canaliculi of the bone-corpuscles had become larger. Otherwise the
corpuscles and their canaliculi were very distinct.” So that with bone
subjected to artificial gastric juice complete decalcification precedes
the dissolution of the fibrous basis. Dr. Burdon Sanderson suggested to
me that the failure of Drosera to digest the fibrous basis of bone,
enamel, and dentine, might be due to the acid being consumed in the
decomposition of the earthy salts, so that there was none left for the
work of digestion. Accordingly, my son thoroughly decalcified the bone
of a sheep with weak hydrochloric acid; and seven minute fragments of
the fibrous basis were placed on so many leaves, four of the fragments
being first damped with saliva to aid prompt inflection. All seven
leaves became inflected, but only very moderately, in the course of a
day. [page 109] They quickly began to re-expand; five of them on the
second day, and the other two on the third day. On all seven leaves the
fibrous tissue was converted into perfectly transparent, viscid, more
or less liquefied little masses. In the middle, however, of one, my son
saw under a high power a few corpuscles, with traces of fibrillation in
the surrounding transparent matter. From these facts it is clear that
the leaves are very little excited by the fibrous basis of bone, but
that the secretion easily and quickly liquefies it, if thoroughly
decalcified. The glands which had remained in contact for two or three
days with the viscid masses were not discoloured, and apparently had
absorbed little of the liquefied tissue, or had been little affected by
it.

Phosphate of Lime.—As we have seen that the tentacles of the first set
of leaves remained clasped for nine or ten days over minute fragments
of bone, and the tentacles of the second set for six or seven days over
the same fragments, I was led to suppose that it was the phosphate of
lime, and not any included animal matter, which caused such long
continued inflection. It is at least certain from what has just been
shown that this cannot have been due to the presence of the fibrous
basis. With enamel and dentine (the former of which contains only 4 per
cent. of organic matter) the tentacles of two successive sets of leaves
remained inflected altogether for eleven days. In order to test my
belief in the potency of phosphate of lime, I procured some from Prof.
Frankland absolutely free of animal matter and of any acid. A small
quantity moistened with water was placed on the discs of two leaves.
One of these was only slightly affected; the other remained closely
inflected for ten days, when a few of the tentacles began to [page 110]
re-expand, the rest being much injured or killed. I repeated the
experiment, but moistened the phosphate with saliva to insure prompt
inflection; one leaf remained inflected for six days (the little saliva
used would not have acted for nearly so long a time) and then died; the
other leaf tried to re-expand on the sixth day, but after nine days
failed to do so, and likewise died. Although the quantity of phosphate
given to the above four leaves was extremely small, much was left in
every case undissolved. A larger quantity wetted with water was next
placed on the discs of three leaves; and these became most strongly
inflected in the course of 24 hrs. They never re-expanded; on the
fourth day they looked sickly, and on the sixth were almost dead. Large
drops of not very viscid fluid hung from their edges during the six
days. This fluid was tested each day with litmus paper, but never
coloured it; and this circumstance I do not understand, as the
superphosphate of lime is acid. I suppose that some superphosphate must
have been formed by the acid of the secretion acting on the phosphate,
but that it was all absorbed and injured the leaves; the large drops
which hung from their edges being an abnormal and dropsical secretion.
Anyhow, it is manifest that the phosphate of lime is a most powerful
stimulant. Even small doses are more or less poisonous, probably on the
same principle that raw meat and other nutritious substances, given in
excess, kill the leaves. Hence the conclusion, that the long continued
inflection of the tentacles over fragments of bone, enamel, and
dentine, is caused by the presence of phosphate of lime, and not of any
included animal matter, is no doubt correct.

Gelatine.—I used pure gelatine in thin sheets given [page 111] me by
Prof. Hoffmann. For comparison, squares of the same size as those
placed on the leaves were left close by on wet moss. These soon
swelled, but retained their angles for three days; after five days they
formed rounded, softened masses, but even on the eighth day a trace of
gelatine could still be detected. Other squares were immersed in water,
and these, though much swollen, retained their angles for six days.
Squares of 1/10 of an inch (2.54 mm.), just moistened with water, were
placed on two leaves; and after two or three days nothing was left on
them but some acid viscid fluid, which in this and other cases never
showed any tendency to regelatinise; so that the secretion must act on
the gelatine differently to what water does, and apparently in the same
manner as gastric juice.* Four squares of the same size as before were
then soaked for three days in water, and placed on large leaves; the
gelatine was liquefied and rendered acid in two days, but did not
excite much inflection. The leaves began to re-expand after four or
five days, much viscid fluid being left on their discs, as if but
little had been absorbed. One of these leaves, as soon as it
re-expanded, caught a small fly, and after 24 hrs. was closely
inflected, showing how much more potent than gelatine is the animal
matter absorbed from an insect. Some larger pieces of gelatine, soaked
for five days in water, were next placed on three leaves, but these did
not become much inflected until the third day; nor was the gelatine
completely liquefied until the fourth day. On this day one leaf began
to re-expand; the second on the fifth; and third on the sixth. These
several facts

* Dr. Lauder Brunton, ‘Handbook for the Phys. Laboratory,’ 1873, pp.
477, 487; Schiff, ‘Leçons phys. de la Digestion,’ 1867, p. 249. [page
112]

prove that gelatine is far from acting energetically on Drosera.

In the last chapter it was shown that a solution of isinglass of
commerce, as thick as milk or cream, induces strong inflection. I
therefore wished to compare its action with that of pure gelatine.
Solutions of one part of both substances to 218 of water were made; and
half-minim drops (.0296 ml.) were placed on the discs of eight leaves,
so that each received 1/480 of a grain, or .135 mg. The four with the
isinglass were much more strongly inflected than the other four. I
conclude therefore that isinglass contains some, though perhaps very
little, soluble albuminous matter. As soon as these eight leaves
re-expanded, they were given bits of roast meat, and in some hours all
became greatly inflected; again showing how much more meat excites
Drosera than does gelatine or isinglass. This is an interesting fact,
as it is well known that gelatine by itself has little power of
nourishing animals.*

Chondrin.—This was sent me by Dr. Moore in a gelatinous state. Some was
slowly dried, and a small chip was placed on a leaf, and a much larger
chip on a second leaf. The first was liquefied in a day; the larger
piece was much swollen and softened, but was not completely liquefied
until the third day. The undried jelly was next tried, and as a control
experiment small cubes were left in water for four days and retained
their angles. Cubes of the same size were placed on two leaves, and
larger cubes on two other leaves. The tentacles and laminae of the
latter were closely inflected after 22 hrs., but those of the

* Dr. Lauder Brunton gives in the ‘Medical Record,’ January 1873, p.
36, an account of Voit’s view of the indirect part which gelatine plays
in nutrition. [page 113]

two leaves with the smaller cubes only to a moderate degree. The jelly
on all four was by this time liquefied, and rendered very acid. The
glands were blackened from the aggregation of their protoplasmic
contents. In 46 hrs. from the time when the jelly was given, the leaves
had almost re-expanded, and completely so after 70 hrs.; and now only a
little slightly adhesive fluid was left unabsorbed on their discs.

One part of chondrin jelly was dissolved in 218 parts of boiling water,
and half-minim drops were given to four leaves; so that each received
about 1/480 of a grain (.135 mg.) of the jelly; and, of course, much
less of dry chondrin. This acted most powerfully, for after only 3 hrs.
30 m. all four leaves were strongly inflected. Three of them began to
re-expand after 24 hrs., and in 48 hrs. were completely open; but the
fourth had only partially re-expanded. All the liquefied chondrin was
by this time absorbed. Hence a solution of chondrin seems to act far
more quickly and energetically than pure gelatine or isinglass; but I
am assured by good authorities that it is most difficult, or
impossible, to know whether chondrin is pure, and if it contained any
albuminous compound, this would have produced the above effects.
Nevertheless, I have thought these facts worth giving, as there is so
much doubt on the nutritious value of gelatine; and Dr. Lauder Brunton
does not know of any experiments with respect to animals on the
relative value of gelatine and chondrin.

Milk.—We have seen in the last chapter that milk acts most powerfully
on the leaves; but whether this is due to the contained casein or
albumen, I know not. Rather large drops of milk excite so much
secretion (which is very acid) that it sometimes trickles down [page
114] from the leaves, and this is likewise characteristic of chemically
prepared casein. Minute drops of milk, placed on leaves, were
coagulated in about ten minutes. Schiff denies* that the coagulation of
milk by gastric juice is exclusively due to the acid which is present,
but attributes it in part to the pepsin; and it seems doubtful whether
with Drosera the coagulation can be wholly due to the acid, as the
secretion does not commonly colour litmus paper until the tentacles
have become well inflected; whereas the coagulation commences, as we
have seen, in about ten minutes. Minute drops of skimmed milk were
placed on the discs of five leaves; and a large proportion of the
coagulated matter or curd was dissolved in 6 hrs. and still more
completely in 8 hrs. These leaves re-expanded after two days, and the
viscid fluid left on their discs was then carefully scraped off and
examined. It seemed at first sight as if all the casein had not been
dissolved, for a little matter was left which appeared of a whitish
colour by reflected light. But this matter, when examined under a high
power, and when compared with a minute drop of skimmed milk coagulated
by acetic acid, was seen to consist exclusively of oil-globules, more
or less aggregated together, with no trace of casein. As I was not
familiar with the microscopical appearance of milk, I asked Dr. Lauder
Brunton to examine the slides, and he tested the globules with ether,
and found that they were dissolved. We may, therefore, conclude that
the secretion quickly dissolves casein, in the state in which it exists
in milk.

Chemically Prepared Casein.—This substance, which

* ‘Leçons,’ &c. tom. ii. page 151. [page 115]

is insoluble in water, is supposed by many chemists to differ from the
casein of fresh milk. I procured some, consisting of hard globules,
from Messrs. Hopkins and Williams, and tried many experiments with it.
Small particles and the powder, both in a dry state and moistened with
water, caused the leaves on which they were placed to be inflected very
slowly, generally not until two days had elapsed. Other particles,
wetted with weak hydrochloric acid (one part to 437 of water) acted in
a single day, as did some casein freshly prepared for me by Dr. Moore.
The tentacles commonly remained inflected for from seven to nine days;
and during the whole of this time the secretion was strongly acid. Even
on the eleventh day some secretion left on the disc of a fully
re-expanded leaf was strongly acid. The acid seems to be secreted
quickly, for in one case the secretion from the discal glands, on which
a little powdered casein had been strewed, coloured litmus paper,
before any of the exterior tentacles were inflected.

Small cubes of hard casein, moistened with water, were placed on two
leaves; after three days one cube had its angles a little rounded, and
after seven days both consisted of rounded softened masses, in the
midst of much viscid and acid secretion; but it must not be inferred
from this fact that the angles were dissolved, for cubes immersed in
water were similarly acted on. After nine days these leaves began to
re-expand, but in this and other cases the casein did not appear, as
far as could be judged by the eye, much, if at all, reduced in bulk.
According to Hoppe-Seyler and Lubavin* casein consists of an
albuminous, with

* Dr. Lauder Brunton, ‘Handbook for Phys. Lab.’ p. 529. [page 116]

a non-albuminous, substance; and the absorption of a very small
quantity of the former would excite the leaves, and yet not decrease
the casein to a perceptible degree. Schiff asserts*—and this is an
important fact for us—that “la casine purifie des chemistes est un
corps presque compltement inattaquable par le suc gastrique.” So that
here we have another point of accordance between the secretion of
Drosera and gastric juice, as both act so differently on the fresh
casein of milk, and on that prepared by chemists.

A few trials were made with cheese; cubes of 1/20 of an inch (1.27 mm.)
were placed on four leaves, and these after one or two days became well
inflected, their glands pouring forth much acid secretion. After five
days they began to re-expand, but one died, and some of the glands on
the other leaves were injured. Judging by the eye, the softened and
subsided masses of cheese, left on the discs, were very little or not
at all reduced in bulk. We may, however, infer from the time during
which the tentacles remained inflected,—from the changed colour of some
of the glands,—and from the injury done to others, that matter had been
absorbed from the cheese.

Legumin.—I did not procure this substance in a separate state; but
there can hardly be a doubt that it would be easily digested, judging
from the powerful effect produced by drops of a decoction of green
peas, as described in the last chapter. Thin slices of a dried pea,
after being soaked in water, were placed on two leaves; these became
somewhat inflected in the course of a single hour, and most strongly so
in 21 hrs. They re-expanded after three or four days.

* ‘Leçons’ &c. tom. ii. page 153. [page 117]

The slices were not liquefied, for the walls of the cells, composed of
cellulose, are not in the least acted on by the secretion.

Pollen.—A little fresh pollen from the common pea was placed on the
discs of five leaves, which soon became closely inflected, and remained
so for two or three days.

The grains being then removed, and examined under the microscope, were
found discoloured, with the oil-globules remarkably aggregated. Many
had their contents much shrunk, and some were almost empty. In only a
few cases were the pollen-tubes emitted. There could be no doubt that
the secretion had penetrated the outer coats of the grains, and had
partially digested their contents. So it must be with the gastric juice
of the insects which feed on pollen, without masticating it.* Drosera
in a state of nature cannot fail to profit to a certain extent by this
power of digesting pollen, as innumerable grains from the carices,
grasses, rumices, fir-trees, and other wind-fertilised plants, which
commonly grow in the same neighbourhood, will be inevitably caught by
the viscid secretion surrounding the many glands.

Gluten.—This substance is composed of two albuminoids, one soluble, the
other insoluble in alcohol.** Some was prepared by merely washing
wheaten flour in water. A provisional trial was made with rather large
pieces placed on two leaves; these, after 21 hrs., were closely
inflected, and remained so for four days, when one was killed and the
other had its glands extremely blackened, but was not afterwards
observed.

* Mr. A.W. Bennett found the undigested coats of the grains in the
intestinal canal of pollen-eating Diptera; see ‘Journal of Hort. Soc.
of London,’ vol. iv. 1874, p. 158.

** Watts’ ‘Dict. of Chemistry,’ vol. ii. 1872, p. 873. [page 118]

Smaller bits were placed on two leaves; these were only slightly
inflected in two days, but afterwards became much more so. Their
secretion was not so strongly acid as that of leaves excited by casein.
The bits of gluten, after lying for three days on the leaves, were more
transparent than other bits left for the same time in water. After
seven days both leaves re-expanded, but the gluten seemed hardly at all
reduced in bulk. The glands which had been in contact with it were
extremely black. Still smaller bits of half putrid gluten were now
tried on two leaves; these were well inflected in 24 hrs., and
thoroughly in four days, the glands in contact being much blackened.
After five days one leaf began to re-expand, and after eight days both
were fully re-expanded, some gluten being still left on their discs.
Four little chips of dried gluten, just dipped in water, were next
tried, and these acted rather differently from fresh gluten. One leaf
was almost fully re-expanded in three days, and the other three leaves
in four days. The chips were greatly softened, almost liquefied, but
not nearly all dissolved. The glands which had been in contact with
them, instead of being much blackened, were of a very pale colour, and
many of them were evidently killed.

In not one of these ten cases was the whole of the gluten dissolved,
even when very small bits were given. I therefore asked Dr. Burdon
Sanderson to try gluten in artificial digestive fluid of pepsin with
hydrochloric acid; and this dissolved the whole. The gluten, however,
was acted on much more slowly than fibrin; the proportion dissolved
within four hours being as 40.8 of gluten to 100 of fibrin. Gluten was
also tried in two other digestive fluids, in which hydrochloric acid
was replaced by propionic [page 119] and butyric acids, and it was
completely dissolved by these fluids at the ordinary temperature of a
room. Here, then, at last, we have a case in which it appears that
there exists an essential difference in digestive power between the
secretion of Drosera and gastric juice; the difference being confined
to the ferment, for, as we have just seen, pepsin in combination with
acids of the acetic series acts perfectly on gluten. I believe that the
explanation lies simply in the fact that gluten is too powerful a
stimulant (like raw meat, or phosphate of lime, or even too large a
piece of albumen), and that it injures or kills the glands before they
have had time to pour forth a sufficient supply of the proper
secretion. That some matter is absorbed from the gluten, we have clear
evidence in the length of time during which the tentacles remain
inflected, and in the greatly changed colour of the glands.

At the suggestion of Dr. Sanderson, some gluten was left for 15 hrs. in
weak hydrochloric acid (.02 per cent.), in order to remove the starch.
It became colourless, more transparent, and swollen. Small portions
were washed and placed on five leaves, which were soon closely
inflected, but to my surprise re-expanded completely in 48 hrs. A mere
vestige of gluten was left on two of the leaves, and not a vestige on
the other three. The viscid and acid secretion, which remained on the
discs of the three latter leaves, was scraped off and examined by my
son under a high power; but nothing could be seen except a little dirt,
and a good many starch grains which had not been dissolved by the
hydrochloric acid. Some of the glands were rather pale. We thus learn
that gluten, treated with weak hydrochloric acid, is not so powerful or
so enduring a [page 120] stimulant as fresh gluten, and does not much
injure the glands; and we further learn that it can be digested quickly
and completely by the secretion.

[Globulin or Crystallin.—This substance was kindly prepared for me from
the lens of the eye by Dr. Moore, and consisted of hard, colourless,
transparent fragments. It is said* that globulin ought to “swell up in
water and dissolve, for the most part forming a gummy liquid;” but this
did not occur with the above fragments, though kept in water for four
days. Particles, some moistened with water, others with weak
hydrochloric acid, others soaked in water for one or two days, were
placed on nineteen leaves. Most of these leaves, especially those with
the long soaked particles, became strongly inflected in a few hours.
The greater number re-expanded after three or four days; but three of
the leaves remained inflected during one, two, or three additional
days. Hence some exciting matter must have been absorbed; but the
fragments, though perhaps softened in a greater degree than those kept
for the same time in water, retained all their angles as sharp as ever.
As globulin is an albuminous substance, I was astonished at this
result; and my object being to compare the action of the secretion with
that of gastric juice, I asked Dr. Burdon Sanderson to try some of the
globulin used by me. He reports that “it was subjected to a liquid
containing 0.2 per cent. of hydrochloric acid, and about 1 per cent. of
glycerine extract of the stomach of a dog. It was then ascertained that
this liquid was capable of digesting 1.31 of its weight of unboiled
fibrin in 1 hr.; whereas, during the hour, only 0.141 of the above
globulin was dissolved. In both cases an excess of the substance to be
digested was subjected to the liquid.”** We thus see that within the
same time less than one-ninth by weight of globulin than of fibrin was
dissolved; and bearing in mind that pepsin with acids of the acetic
series has only about one-third of the digestive power of pepsin with
hydrochloric acid, it is not surprising that the fragments of

* Watts’ ‘Dictionary of Chemistry,’ vol. ii. page 874.

** I may add that Dr. Sanderson prepared some fresh globulin by
Schmidt’s method, and of this 0.865 was dissolved within the same time,
namely, one hour; so that it was far more soluble than that which I
used, though less soluble than fibrin, of which, as we have seen, 1.31
was dissolved. I wish that I had tried on Drosera globulin prepared by
this method. [page 121]

globulin were not corroded or rounded by the secretion of Drosera,
though some soluble matter was certainly extracted from them and
absorbed by the glands.

Haematin.—Some dark red granules, prepared from bullock’s blood, were
given me; these were found by Dr. Sanderson to be insoluble in water,
acids, and alcohol, so that they were probably haematin, together with
other bodies derived from the blood. Particles with little drops of
water were placed on four leaves, three of which were pretty closely
inflected in two days; the fourth only moderately so. On the third day
the glands in contact with the haematin were blackened, and some of the
tentacles seemed injured. After five days two leaves died, and the
third was dying; the fourth was beginning to re-expand, but many of its
glands were blackened and injured. It is therefore clear that matter
had been absorbed which was either actually poisonous or of too
stimulating a nature. The particles were much more softened than those
kept for the same time in water, but, judging by the eye, very little
reduced in bulk. Dr. Sanderson tried this substance with artificial
digestive fluid, in the manner described under globulin, and found that
whilst 1.31 of fibrin, only 0.456 of the haematin was dissolved in an
hour; but the dissolution by the secretion of even a less amount would
account for its action on Drosera. The residue left by the artificial
digestive fluid at first yielded nothing more to it during several
succeeding days.]

_Substances which are not Digested by the Secretion._

All the substances hitherto mentioned cause prolonged inflection of the
tentacles, and are either completely or at least partially dissolved by
the secretion. But there are many other substances, some of them
containing nitrogen, which are not in the least acted on by the
secretion, and do not induce inflection for a longer time than do
inorganic and insoluble objects. These unexciting and indigestible
substances are, as far as I have observed, epidermic productions (such
as bits of human nails, balls of hair, the quills of feathers),
fibro-elastic tissue, mucin, pepsin, urea, chitine, chlorophyll,
cellulose, gun-cotton, fat, oil, and starch. [page 122]

To these may be added dissolved sugar and gum, diluted alcohol, and
vegetable infusions not containing albumen, for none of these, as shown
in the last chapter, excite inflection. Now, it is a remarkable fact,
which affords additional and important evidence, that the ferment of
Drosera is closely similar to or identical with pepsin, that none of
these same substances are, as far as it is known, digested by the
gastric juice of animals, though some of them are acted on by the other
secretions of the alimentary canal. Nothing more need be said about
some of the above enumerated substances, excepting that they were
repeatedly tried on the leaves of Drosera, and were not in the least
affected by the secretion. About the others it will be advisable to
give my experiments.

[Fibro-elastic Tissue.—We have already seen that when little cubes of
meat, &c., were placed on leaves, the muscles, areolar tissue, and
cartilage were completely dissolved, but the fibro-elastic tissue, even
the most delicate threads, were left without the least signs of having
been attacked. And it is well known that this tissue cannot be digested
by the gastric juice of animals.*

Mucin.—As this substance contains about 7 per cent. of nitrogen, I
expected that it would have excited the leaves greatly and been
digested by the secretion, but in this I was mistaken. From what is
stated in chemical works, it appears extremely doubtful whether mucin
can be prepared as a pure principle. That which I used (prepared by Dr.
Moore) was dry and hard. Particles moistened with water were placed on
four leaves, but after two days there was only a trace of inflection in
the immediately adjoining tentacles. These leaves were then tried with
bits of meat, and all four soon became strongly inflected. Some of the
dried mucin was then soaked in water for two days, and little cubes of
the proper size were placed on three leaves. After four days the
tentacles

* See, for instance, Schiff, ‘Phys. de la Digestion,’ 1867, tom. ii.,
p. 38. [page 123]

round the margins of the discs were a little inflected, and the
secretion collected on the disc was acid, but the exterior tentacles
were not affected. One leaf began to re-expand on the fourth day, and
all were fully re-expanded on the sixth. The glands which had been in
contact with the mucin were a little darkened. We may therefore
conclude that a small amount of some impurity of a moderately exciting
nature had been absorbed. That the mucin employed by me did contain
some soluble matter was proved by Dr. Sanderson, who on subjecting it
to artificial gastric juice found that in 1 hr. some was dissolved, but
only in the proportion of 23 to 100 of fibrin during the same time. The
cubes, though perhaps rather softer than those left in water for the
same time, retained their angles as sharp as ever. We may therefore
infer that the mucin itself was not dissolved or digested. Nor is it
digested by the gastric juice of living animals, and according to
Schiff* it is a layer of this substance which protects the coats of the
stomach from being corroded during digestion.

Pepsin.—My experiments are hardly worth giving, as it is scarcely
possible to prepare pepsin free from other albuminoids; but I was
curious to ascertain, as far as that was possible, whether the ferment
of the secretion of Drosera would act on the ferment of the gastric
juice of animals. I first used the common pepsin sold for medicinal
purposes, and afterwards some which was much purer, prepared for me by
Dr. Moore. Five leaves to which a considerable quantity of the former
was given remained inflected for five days; four of them then died,
apparently from too great stimulation. I then tried Dr. Moore’s pepsin,
making it into a paste with water, and placing such small particles on
the discs of five leaves that all would have been quickly dissolved had
it been meat or albumen. The leaves were soon inflected; two of them
began to re-expand after only 20 hrs., and the other three were almost
completely re-expanded after 44 hrs. Some of the glands which had been
in contact with the particles of pepsin, or with the acid secretion
surrounding them, were singularly pale, whereas others were singularly
dark-coloured. Some of the secretion was scraped off and examined under
a high power; and it abounded with granules undistinguishable from
those of pepsin left in water for the same length of time. We may
therefore infer, as highly probable (remembering what small quantities
were given), that the ferment of Drosera does not act on or digest

* ‘Leçons phys. de la Digestion,’ 1867, tom. ii., p. 304. [page 124]

pepsin, but absorbs from it some albuminous impurity which induces
inflection, and which in large quantity is highly injurious. Dr. Lauder
Brunton at my request endeavoured to ascertain whether pepsin with
hydrochloric acid would digest pepsin, and as far as he could judge, it
had no such power. Gastric juice, therefore, apparently agrees in this
respect with the secretion of Drosera.

Urea.—It seemed to me an interesting inquiry whether this refuse of the
living body, which contains much nitrogen, would, like so many other
animal fluids and substances, be absorbed by the glands of Drosera and
cause inflection. Half-minim drops of a solution of one part to 437 of
water were placed on the discs of four leaves, each drop containing the
quantity usually employed by me, namely 1/960 of a grain, or .0674 mg.;
but the leaves were hardly at all affected. They were then tested with
bits of meat, and soon became closely inflected. I repeated the same
experiment on four leaves with some fresh urea prepared by Dr. Moore;
after two days there was no inflection; I then gave them another dose,
but still there was no inflection. These leaves were afterwards tested
with similarly sized drops of an infusion of raw meat, and in 6 hrs.
there was considerable inflection, which became excessive in 24 hrs.
But the urea apparently was not quite pure, for when four leaves were
immersed in 2 dr. (7.1 ml.) of the solution, so that all the glands,
instead of merely those on the disc, were enabled to absorb any small
amount of impurity in solution, there was considerable inflection after
24 hrs., certainly more than would have followed from a similar
immersion in pure water. That the urea, which was not perfectly white,
should have contained a sufficient quantity of albuminous matter, or of
some salt of ammonia, to have caused the above effect, is far from
surprising, for, as we shall see in the next chapter, astonishingly
small doses of ammonia are highly efficient. We may therefore conclude
that urea itself is not exciting or nutritious to Drosera; nor is it
modified by the secretion, so as to be rendered nutritious, for, had
this been the case, all the leaves with drops on their discs assuredly
would have been well inflected. Dr. Lauder Brunton informs me that from
experiments made at my request at St. Bartholomew’s Hospital it appears
that urea is not acted on by artificial gastric juice, that is by
pepsin with hydrochloric acid.

Chitine.—The chitinous coats of insects naturally captured by the
leaves do not appear in the least corroded. Small square pieces of the
delicate wing and of the elytron of a Staphylinus [page 125] were
placed on some leaves, and after these had re-expanded, the pieces were
carefully examined. Their angles were as sharp as ever, and they did
not differ in appearance from the other wing and elytron of the same
insect which had been left in water. The elytron, however, had
evidently yielded some nutritious matter, for the leaf remained clasped
over it for four days; whereas the leaves with bits of the true wing
re-expanded on the second day. Any one who will examine the excrement
of insect-eating animals will see how powerless their gastric juice is
on chitine.

Cellulose.—I did not obtain this substance in a separate state, but
tried angular bits of dry wood, cork, sphagnum moss, linen, and cotton
thread. None of these bodies were in the least attacked by the
secretion, and they caused only that moderate amount of inflection
which is common to all inorganic objects. Gun-cotton, which consists of
cellulose, with the hydrogen replaced by nitrogen, was tried with the
same result. We have seen that a decoction of cabbage-leaves excites
the most powerful inflection. I therefore placed two little square bits
of the blade of a cabbage-leaf, and four little cubes cut from the
midrib, on six leaves of Drosera. These became well inflected in 12
hrs., and remained so for between two and four days; the bits of
cabbage being bathed all the time by acid secretion. This shows that
some exciting matter, to which I shall presently refer, had been
absorbed; but the angles of the squares and cubes remained as sharp as
ever, proving that the framework of cellulose had not been attacked.
Small square bits of spinach-leaves were tried with the same result;
the glands pouring forth a moderate supply of acid secretion, and the
tentacles remaining inflected for three days. We have also seen that
the delicate coats of pollen grains are not dissolved by the secretion.
It is well known that the gastric juice of animals does not attack
cellulose.

Chlorophyll.—This substance was tried, as it contains nitrogen. Dr.
Moore sent me some preserved in alcohol; it was dried, but soon
deliquesced. Particles were placed on four leaves; after 3 hrs. the
secretion was acid; after 8 hrs. there was a good deal of inflection,
which in 24 hrs. became fairly well marked. After four days two of the
leaves began to open, and the other two were then almost fully
re-expanded. It is therefore clear that this chlorophyll contained
matter which excited the leaves to a moderate degree; but judging by
the eye, little or none was dissolved; so that in a pure state it would
not probably have been attacked by the secretion. Dr. Sanderson tried
that which I [page 126] used, as well as some freshly prepared, with
artificial digestive liquid, and found that it was not digested. Dr.
Lauder Brunton likewise tried some prepared by the process given in the
British Pharmacopoeia, and exposed it for five days at the temperature
of 37° Cent. to digestive liquid, but it was not diminished in bulk,
though the fluid acquired a slightly brown colour. It was also tried
with the glycerine extract of pancreas with a negative result. Nor does
chlorophyll seem affected by the intestinal secretions of various
animals, judging by the colour of their excrement.

It must not be supposed from these facts that the grains of
chlorophyll, as they exist in living plants, cannot be attacked by the
secretion; for these grains consist of protoplasm merely coloured by
chlorophyll. My son Francis placed a thin slice of spinach leaf,
moistened with saliva, on a leaf of Drosera, and other slices on damp
cotton-wool, all exposed to the same temperature. After 19 hrs. the
slice on the leaf of Drosera was bathed in much secretion from the
inflected tentacles, and was now examined under the microscope. No
perfect grains of chlorophyll could be distinguished; some were
shrunken, of a yellowish-green colour, and collected in the middle of
the cells; others were disintegrated and formed a yellowish mass,
likewise in the middle of the cells. On the other hand, in the slices
surrounded by damp cotton-wool, the grains of chlorophyll were green
and as perfect as ever. My son also placed some slices in artificial
gastric juice, and these were acted on in nearly the same manner as by
the secretion. We have seen that bits of fresh cabbage and spinach
leaves cause the tentacles to be inflected and the glands to pour forth
much acid secretion; and there can be little doubt that it is the
protoplasm forming the grains of chlorophyll, as well as that lining
the walls of the cells, which excites the leaves.

Fat and Oil.—Cubes of almost pure uncooked fat, placed on several
leaves, did not have their angles in the least rounded. We have also
seen that the oil-globules in milk are not digested. Nor does olive oil
dropped on the discs of leaves cause any inflection; but when they are
immersed in olive oil, they become strongly inflected; but to this
subject I shall have to recur. Oily substances are not digested by the
gastric juice of animals.

Starch.—Rather large bits of dry starch caused well-marked inflection,
and the leaves did not re-expand until the fourth day; but I have no
doubt that this was due to the prolonged irritation of the glands, as
the starch continued to absorb the secretion. The particles were not in
the least reduced in size; [page 127] and we know that leaves immersed
in an emulsion of starch are not at all affected. I need hardly say
that starch is not digested by the gastric juice of animals.

Action of the Secretion on Living Seeds.

The results of some experiments on living seeds, selected by hazard,
may here be given, though they bear only indirectly on our present
subject of digestion.

Seven cabbage seeds of the previous year were placed on the same number
of leaves. Some of these leaves were moderately, but the greater number
only slightly inflected, and most of them re-expanded on the third day.
One, however, remained clasped till the fourth, and another till the
fifth day. These leaves therefore were excited somewhat more by the
seeds than by inorganic objects of the same size. After they
re-expanded, the seeds were placed under favourable conditions on damp
sand; other seeds of the same lot being tried at the same time in the
same manner, and found to germinate well. Of the seven seeds which had
been exposed to the secretion, only three germinated; and one of the
three seedlings soon perished, the tip of its radicle being from the
first decayed, and the edges of its cotyledons of a dark brown colour;
so that altogether five out of the seven seeds ultimately perished.

Radish seeds (Raphanus sativus) of the previous year were placed on
three leaves, which became moderately inflected, and re-expanded on the
third or fourth day. Two of these seeds were transferred to damp sand;
only one germinated, and that very slowly. This seedling had an
extremely short, crooked, diseased, radicle, with no absorbent hairs;
and the cotyledons were oddly mottled with purple, with the edges
blackened and partly withered.

Cress seeds (Lepidum sativum) of the previous year were placed on four
leaves; two of these next morning were moderately and two strongly
inflected, and remained so for four, five, and even six days. Soon
after these seeds were placed on the leaves and had become damp, they
secreted in the usual manner a layer of tenacious mucus; and to
ascertain whether it was the absorption of this substance by the glands
which caused so much inflection, two seeds were put into water, and as
much of the mucus as possible scraped off. They were then placed on
leaves, which became very strongly inflected in the course of 3 hrs.,
and were still closely inflected on the third day; so that it evidently
was not the mucus which excited so [page 128] much inflection; on the
contrary, this served to a certain extent as a protection to the seeds.
Two of the six seeds germinated whilst still lying on the leaves, but
the seedlings, when transferred to damp sand, soon died; of the other
four seeds, only one germinated.

Two seeds of mustard (Sinapis nigra), two of celery (Apium
graveolens)—both of the previous year, two seeds well soaked of caraway
(Carum carui), and two of wheat, did not excite the leaves more than
inorganic objects often do. Five seeds, hardly ripe, of a buttercup
(Ranunculus), and two fresh seeds of Anemone nemorosa, induced only a
little more effect. On the other hand, four seeds, perhaps not quite
ripe, of Carex sylvatica caused the leaves on which they were placed to
be very strongly inflected; and these only began to re-expand on the
third day, one remaining inflected for seven days.

It follows from these few facts that different kinds of seeds excite
the leaves in very different degrees; whether this is solely due to the
nature of their coats is not clear. In the case of the cress seeds, the
partial removal of the layer of mucus hastened the inflection of the
tentacles. Whenever the leaves remain inflected during several days
over seeds, it is clear that they absorb some matter from them. That
the secretion penetrates their coats is also evident from the large
proportion of cabbage, raddish, and cress seeds which were killed, and
from several of the seedlings being greatly injured. This injury to the
seeds and seedlings may, however, be due solely to the acid of the
secretion, and not to any process of digestion; for Mr. Traherne
Moggridge has shown that very weak acids of the acetic series are
highly injurious to seeds. It never occurred to me to observe whether
seeds are often blown on to the viscid leaves of plants growing in a
state of nature; but this can hardly fail sometimes to occur, as we
shall hereafter see in the case of Pinguicula. If so, Drosera will
profit to a slight degree by absorbing matter from such seeds.]

A Summary and Concluding Remarks on the Digestive Power of Drosera.

When the glands on the disc are excited either by the absorption of
nitrogenous matter or by mechanical irritation, their secretion
increases in quantity and becomes acid. They likewise transmit [page
129] some influence to the glands of the exterior tentacles, causing
them to secrete more copiously; and their secretion likewise becomes
acid. With animals, according to Schiff,* mechanical irritation excites
the glands of the stomach to secrete an acid, but not pepsin. Now, I
have every reason to believe (though the fact is not fully
established), that although the glands of Drosera are continually
secreting viscid fluid to replace that lost by evaporation, yet they do
not secrete the ferment proper for digestion when mechanically
irritated, but only after absorbing certain matter, probably of a
nitrogenous nature. I infer that this is the case, as the secretion
from a large number of leaves which had been irritated by particles of
glass placed on their discs did not digest albumen; and more especially
from the analogy of Dionaea and Nepenthes. In like manner, the glands
of the stomach of animals secrete pepsin, as Schiff asserts, only after
they have absorbed certain soluble substances, which he designates as
peptogenes. There is, therefore, a remarkable parallelism between the
glands of Drosera and those of the stomach in the secretion of their
proper acid and ferment.

The secretion, as we have seen, completely dissolves albumen, muscle,
fibrin, areolar tissue, cartilage, the fibrous basis of bone, gelatine,
chondrin, casein in the state in which it exists in milk, and gluten
which has been subjected to weak hydrochloric acid. Syntonin and
legumin excite the leaves so powerfully and quickly that there can
hardly be a doubt that both would be dissolved by the secretion. The
secretion

* ‘Phys. de la Digestion,’ 1867, tom. ii. pp. 188, 245. [page 130]

failed to digest fresh gluten, apparently from its injuring the glands,
though some was absorbed. Raw meat, unless in very small bits, and
large pieces of albumen, &c., likewise injure the leaves, which seem to
suffer, like animals, from a surfeit. I know not whether the analogy is
a real one, but it is worth notice that a decoction of cabbage leaves
is far more exciting and probably nutritious to Drosera than an
infusion made with tepid water; and boiled cabbages are far more
nutritious, at least to man, than the uncooked leaves. The most
striking of all the cases, though not really more remarkable than many
others, is the digestion of so hard and tough a substance as cartilage.
The dissolution of pure phosphate of lime, of bone, dentine, and
especially enamel, seems wonderful; but it depends merely on the
long-continued secretion of an acid; and this is secreted for a longer
time under these circumstances than under any others. It was
interesting to observe that as long as the acid was consumed in
dissolving the phosphate of lime, no true digestion occurred; but that
as soon as the bone was completely decalcified, the fibrous basis was
attacked and liquefied with the greatest ease. The twelve substances
above enumerated, which are completely dissolved by the secretion, are
likewise dissolved by the gastric juice of the higher animals; and they
are acted on in the same manner, as shown by the rounding of the angles
of albumen, and more especially by the manner in which the transverse
striae of the fibres of muscle disappear.

The secretion of Drosera and gastric juice were both able to dissolve
some element or impurity out of the globulin and haematin employed by
me. The secretion also dissolved something out of chemically [page 131]
prepared casein, which is said to consist of two substances; and
although Schiff asserts that casein in this state is not attacked by
gastric juice, he might easily have overlooked a minute quantity of
some albuminous matter, which Drosera would detect and absorb. Again,
fibro-cartilage, though not properly dissolved, is acted on in the same
manner, both by the secretion of Drosera and gastric juice. But this
substance, as well as the so-called haematin used by me, ought perhaps
to have been classed with indigestible substances.

That gastric juice acts by means of its ferment, pepsin, solely in the
presence of an acid, is well established; and we have excellent
evidence that a ferment is present in the secretion of Drosera, which
likewise acts only in the presence of an acid; for we have seen that
when the secretion is neutralised by minute drops of the solution of an
alkali, the digestion of albumen is completely stopped, and that on the
addition of a minute dose of hydrochloric acid it immediately
recommences.

The nine following substances, or classes of substances, namely,
epidermic productions, fibro-elastic tissue, mucin, pepsin, urea,
chitine, cellulose, gun-cotton, chlorophyll, starch, fat and oil, are
not acted on by the secretion of Drosera; nor are they, as far as is
known, by the gastric juice of animals. Some soluble matter, however,
was extracted from the mucin, pepsin, and chlorophyll, used by me, both
by the secretion and by artificial gastric juice.

The several substances, which are completely dissolved by the
secretion, and which are afterwards absorbed by the glands, affect the
leaves rather differently. They induce inflection at very different
[page 132] rates and in very different degrees; and the tentacles
remain inflected for very different periods of time. Quick inflection
depends partly on the quantity of the substance given, so that many
glands are simultaneously affected, partly on the facility with which
it is penetrated and liquefied by the secretion, partly on its nature,
but chiefly on the presence of exciting matter already in solution.
Thus saliva, or a weak solution of raw meat, acts much more quickly
than even a strong solution of gelatine. So again leaves which have
re-expanded, after absorbing drops of a solution of pure gelatine or
isinglass (the latter being the more powerful of the two), if given
bits of meat, are inflected much more energetically and quickly than
they were before, notwithstanding that some rest is generally requisite
between two acts of inflection. We probably see the influence of
texture in gelatine and globulin when softened by having been soaked in
water acting more quickly than when merely wetted. It may be partly due
to changed texture, and partly to changed chemical nature, that
albumen, which had been kept for some time, and gluten which had been
subjected to weak hydrochloric acid, act more quickly than these
substances in their fresh state.

The length of time during which the tentacles remain inflected largely
depends on the quantity of the substance given, partly on the facility
with which it is penetrated or acted on by the secretion, and partly on
its essential nature. The tentacles always remain inflected much longer
over large bits or large drops than over small bits or drops. Texture
probably plays a part in determining the extraordinary length of time
during which the tentacles remain inflected [page 133] over the hard
grains of chemically prepared casein. But the tentacles remain
inflected for an equally long time over finely powdered, precipitated
phosphate of lime; phosphorus in this latter case evidently being the
attraction, and animal matter in the case of casein. The leaves remain
long inflected over insects, but it is doubtful how far this is due to
the protection afforded by their chitinous integuments; for animal
matter is soon extracted from insects (probably by exosmose from their
bodies into the dense surrounding secretion), as shown by the prompt
inflection of the leaves. We see the influence of the nature of
different substances in bits of meat, albumen, and fresh gluten acting
very differently from equal-sized bits of gelatine, areolar tissue, and
the fibrous basis of bone. The former cause not only far more prompt
and energetic, but more prolonged, inflection than do the latter. Hence
we are, I think, justified in believing that gelatine, areolar tissue,
and the fibrous basis of bone, would be far less nutritious to Drosera
than such substances as insects, meat, albumen, &c. This is an
interesting conclusion, as it is known that gelatine affords but little
nutriment to animals; and so, probably, would areolar tissue and the
fibrous basis of bone. The chondrin which I used acted more powerfully
than gelatine, but then I do not know that it was pure. It is a more
remarkable fact that fibrin, which belongs to the great class of
Proteids,* including albumen in one of its sub-groups, does not excite
the tentacles in a greater degree, or keep them inflected for a longer
time, than does gelatine, or

* See the classification adopted by Dr. Michael Foster in Watts’
‘Dictionary of Chemistry,’ Supplement 1872, page 969. [page 134]

areolar tissue, or the fibrous basis of bone. It is not known how long
an animal would survive if fed on fibrin alone, but Dr. Sanderson has
no doubt longer than on gelatine, and it would be hardly rash to
predict, judging from the effects on Drosera, that albumen would be
found more nutritious than fibrin. Globulin likewise belongs to the
Proteids, forming another sub-group, and this substance, though
containing some matter which excited Drosera rather strongly, was
hardly attacked by the secretion, and was very little or very slowly
attacked by gastric juice. How far globulin would be nutritious to
animals is not known. We thus see how differently the above specified
several digestible substances act on Drosera; and we may infer, as
highly probable, that they would in like manner be nutritious in very
different degrees both to Drosera and to animals.

The glands of Drosera absorb matter from living seeds, which are
injured or killed by the secretion. They likewise absorb matter from
pollen, and from fresh leaves; and this is notoriously the case with
the stomachs of vegetable-feeding animals. Drosera is properly an
insectivorous plant; but as pollen cannot fail to be often blown on to
the glands, as will occasionally the seeds and leaves of surrounding
plants, Drosera is, to a certain extent, a vegetable-feeder.

Finally, the experiments recorded in this chapter show us that there is
a remarkable accordance in the power of digestion between the gastric
juice of animals with its pepsin and hydrochloric acid and the
secretion of Drosera with its ferment and acid belonging to the acetic
series. We can, therefore, hardly doubt that the ferment in both cases
is closely similar, [page 135] if not identically the same. That a
plant and an animal should pour forth the same, or nearly the same,
complex secretion, adapted for the same purpose of digestion, is a new
and wonderful fact in physiology. But I shall have to recur to this
subject in the fifteenth chapter, in my concluding remarks on the
Droseraceae. [page 136]