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was present. In the remaining eight there was some evidence of an acid reaction, but this was exceedingly feeble and sometimes doubtful. The case is very different with glands which are excited by the contact of solid substances, either organic or inorganic. Fourteen leaves, in which the secretion was free from any perceptible trace of acidity, were treated, some with particles of broken glass, others with cubes of coagulated albumen, others with bits of raw meat; and when, after twenty-four hours, their tentacles had become more or less completely inflected, the secretion was found to be distinctly acid. The secretion becomes acid, not only on the glands at the centre of the leaf where the foreign substances are placed, but also on those of the marginal tentacles while yet in process of inflection, before they have reached the central part, and consequently before they have themselves touched the exciting substance. Thus the stimulus which causes secretion, as well as that which produces movement, may be transmitted from one part of the leaf to another, through the intervening tissues. Mr. Darwin testifies that he has tried “hundreds of times” the secretion on the disks of leaves which were inflected over various objects, and has never failed to find it acid. action increases in intensity after the tentacles have remained for some time closed over a foreign substance.
The specific character of the acid thus produced was not fully ascertained. Various trials were made by Professor Frankland to determine its nature, but without complete success, owing to the small quantity obtainable for experiment. It was shown, however, to be neither hydrochloric, sulphuric, oxalic, tartaric, nor formic acid. The evidence on the whole indicated that it was probably an organic acid, similar in character to the acetic or the fatty acids.
The effect of the continued action of this acid secretion upon solid nutritious substances is that they become softened and dissolved, and the liquefied materials are afterward absorbed. The method used for investigating this point was similar to that employed in experiments with the gastric juice of animals. Small cubes of coagulated albumen, with their edges and angles sharply cut, were placed upon the leaves and examined at various times after having been clasped by the tentacles. After some hours their edges and angles were rounded off, the masses themselves being enveloped in a transparent fluid. In about two days they were often completely liquefied; and later still both the cubes and the fluid had disappeared. Bits of coagulated fibrin, of delicate areolar tissue, and even of cartilage, were affected in a similar
way. Small pieces of roasted meat were softened and liquefied from the surface inward, the muscular tissue being gradually
disintegrated and the fibres losing their characteristic transverse striations. As a rule, the albuminous and albuminoid substances, and digestible tissues composed of them, were found to undergo liquefaction; while the epidermic tissues, such as nails, hair, and feathers, and non-nitrogenous organic matters, such as solid fat, starch-grains, and cellulose, were unaffected, though left in contact with the leaves for four or five days. The acid secretion of the Sundew accordingly shows a striking analogy, both in its properties and action, with the gastric juice of animals, which is also acid, and which digests albuminous matters, but leaves starch and cellulose unchanged.
The analogy is carried still further by the fact that its acid reaction is essential to the digestive power of the Sundew secretion; and that this power may be temporarily arrested by neutralizing its acidity, and again brought into action by the addition of another acid. Solutions of carbonate of soda were used for the purpose of neutralizing the acid reaction, and dilute hydrochloric acid for restoring it. Cubes of albumen, which remained in the first case unaltered for twentyfour hours, were nearly or quite dissolved by the next day, after the secretion was again made acid.
Thus it appears that the plant not only seizes and holds animal matters brought in contact with its leaves, but it also digests them; that is, reduces them to the liquid form in which they are fitted for absorption. The author believes that the secretion by which this is accomplished resembles in all respects the gastric juice of animals; that it acts by virtue of containing a ferment like the pepsin of the gastric juice; and that, as he expresses it, the ferment in both cases is closely similar, if not identically the same.
This, we think, is doubtful. Indeed Mr. Darwin, in this part of his book, seems to have been led into a singular confusion with regard to the combined action of an acid and a ferment, and the experimental evidences of their existence. On page 94 he says: “ The best and almost sole test of the presence of some ferment analogous to pepsin in the secretion appeared to be to neutralize 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 to observe whether the process recommenced. This was done, and, as we shall see, with success."
And again, on page 96: "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 neutralized 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."
It is hardly necessary to say that these experiments do not prove in the least the existence of a ferment in the secretion of Drosera. They only show that the presence of an acid is essential to its digestive action, which is suspended if it be rendered neutral or alkaline. In the gastric juice of animals, the pepsin, or organic ferment, may be thrown down as a visible precipitate by the action of heat or of alcohol. The secretion, thus deprived of its pepsin, is powerless for digestion, though it may still be acid; and the pepsin-precipitate, when redissolved in water, will again exert its digestive power, if the solution be slightly acidulated. This palpable demonstration of a ferment in the gastric juice, as equally essential with its acid ingredient, is wanting in the case of the Sundew secretion. It might be difficult to carry out such an experiment with the secretion of Drosera, owing to the minute quantity to be obtained. Mr. Darwin cut off a large number of leaves which had been moderately excited by the contact of pounded glass, and obtained from them a watery extract of slightly acid reaction, which he tested by immersing in it cubes of albumen, to see whether they would be digested, but without success. He accounts for the failure by supposing that the secretion of the ferment requires a previous absorption by the glands of soluble animal matter ; but, at all events, it was not obtained in this way. The only evidence for the existence of a ferment in the secretion of the Sundew
appears to be the fact that this secretion will dissolve small quantities of solid albuminous matters; and these substances are digested, so far as we know in animals, only by aid of such a ferment. But this evidence is hardly more than inferential.
In point of fact, digestion by the gastric juice, in animals, is something more than a simple solution. The albuminous matters are not merely liquefied. They are chemically changed, and converted into a new substance, the so-called “albuminose or peptone; and this substance is distinguishable from albumen or fibrin by definite characters. Coagulated fibrin, if subjected to the action of a dilute acid alone, with the aid of continuous warmth, will be softened and gelatinized, and after a time dissolved; but it is not converted into albuminose, and may be precipitated again by neutralizing the fluid with an alkali.
On the other hand, if pepsin be present it undergoes a true digestion, and is no longer precipitable by an alkali. This is an essential feature of the digestive process, and is important for the nutrition of the animal. For if the digested matters in the stomach
that the Sundew leaves certainly injure seeds left in contact with
were simply held in solution by an acid fluid, when absorbed into the circulation they would be precipitated by contact with the plasma of the blood, which is alkaline. It is possible that in plants this necessity does not exist, since the juices of the vegetable parenchyma have generally or always an acid reaction.
All things considered, we cannot help thinking that the analogy between the secretion of Drosera and the gastric juice of animals, in Mr. Darwin's book, is too closely drawn. They are no doubt alike in function, so far as regards the disintegration and liquefaction of nutritious material. But their identity of composition is far from being demonstrated ; and especially the evidence of an organic ferment in the vegetable secretion is very imperfect, as compared with that of pepsin in the gastric juice.
The whole subject of the capture and digestion of insects by plants is a most interesting one, and shows another remarkable relation between the two organic kingdoms. Insects suck the juices of plants, and lay their eggs in the leaves or under the bark, and so take their pay for services rendered in fertilizing the flowers. But plants also devour insects, and make up for their scanty roots or insufficient soil by absorbing albuminous matter ready made from the bodies of their victims. Do plants also feed upon each other? Mr. Darwin found
them, perhaps by absorbing some of their organic ingredients. This is still more probable in the case of Pinguicula, or Butterwort; the leaves of which, by means of their viscid secretion, catch not only insects, but many leaves and seeds belonging to other plants. Several specimens, gathered at the same time, were found to have sixteen seeds, belonging to nine different species, adhering to fourteen of their leaves. Seeds of the cabbage and other kinds, applied to the leaves of Pinguicula, caused inflection and active secretion from the glands; and there was evidence, not only that the seeds were injured, and in many cases killed, but that the glands had absorbed from them some substances which were no doubt to be used for the nutrition of the plant.
The marauding habits of Drosera and other vegetables, so fully described by the author of "Insectivorous Plants,” suggest another consideration in regard to insects which prey upon each other. The Sundew spreads out its sensitive tentacles in the air ; and when some passing fly has alighted on its disk and become entangled in the secretion, they close over his body with mathematical precision and suck out its nutritious juices for their own benefit. The little ant-lion digs a circular pitfall in the live sand, and lies in wait at the bottom
until some incautious intruder has found his way in; and, when his strength has been exhausted in vain struggles to escape, seizes and devours him. Is not the plan thus laid for capturing insect prey an inevitable result of the organization of the animal as well as of the plant; and is it not carried out by a sort of physiological fatality, as imperative in the one case as in the other?
4.- Lorenzo de' Medici il Magnifico. Von. ALFRED von REUMONT.
Leipzig. 1874. 2 vols. 8vo. pp. xxiii., 606; xviii., 604.
At the close of the last century a Liverpool attorney published a life of the great Florentine banker, statesman, and poet, known in history as Lorenzo de' Medici, which has since enjoyed a popularity seldom reached even by works of far greater merit. The novelty of the subject, but even more the novelty of the treatment, contributed to make Mr. Roscoe's success as splendid as durable, both at home and abroad, for he may fairly be said to have introduced to the Italians one of their greatest men. In spite of many grave defects, this work will doubtless long remain one of the most entertaining historical monographs in the language. Its distinguishing feature is a judicious blending of the political, social, and literary elements of the period, producing a picture of great brilliance and interest, but which is to good history what Dubufe's Prodigal Son, for instance, is to good art. The utterly false conception which Mr. Roscoe conveys of his hero has already been fully exposed by Sismondi, and later by Villari - whose views have been reproduced by Trollope in his history of Florence, and the new methods of political and literary history have long ago outstripped a work, the best part of which is but second-hand and incomplete. The interest of the period itself remained, and continued the popularity of a book for which no better substitute could be found.
This interest has, if possible, increased of late years, as the importance of the Italian Renaissance for literature and art has been more clearly recognized, so that a new work on Lorenzo de' Medici could not have appeared at a more opportune time. Von Reumont's book fills the want long felt of an exhaustive treatise upon the political, social, and literary phases of Italian (and, in a more restricted sense,
* In his Storia di Girolamo Savonarola e de suoi tempi (2 vols. Florence: Le Monnier), of which there is an excellent translation by Horner in the History of Girolamo Savonarola and of his Times. 2 vols. London: Longman & Green, 1863. VOL. CXXIII. NO. 251.