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.

[Experiment 1.

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]