insects, but they secrete a gastric juice which digests them. Nägeli has shown the presence of pepsin in yeast-cells, and attention has lately been called by Wurtz and others to the juice of the Carica papaya, which contains a pepsin-like substance capable of peptonizing fibrine completely. Moreover, there is the closest similarity between diastase and ptyaline; and the milk of the cow-tree, recently examined by Boussingault and found to resemble cream closely in composition, shows the presence of an emulsifying agent in the vegetable kingdom analogous to pancreatine in the animal.
Another most curious proof of the identity of animal and vegetable protoplasm has been given by Claude Bernard, who has shown that both are alike sensitive to the influence of anæsthetics. A sensitive plant exposed to ether no longer closed its leaflets when touched. Assimilation and growth, as well as germination, are arrested by chloroform. The yeast-plant when etherized no longer decomposes sugar to produce alcohol and carbon dioxide; while the inversive and non-vital ferment still acts to convert the cane-sugar into glucose; precisely as under these circumstances the diastasic ferment converts the starch of the seed into sugar. By arresting anæsthetically the process by which carbon dioxide is absorbed and oxygen evolved, the true respiratory process, being less affected, now appears; and Schützenberger has proved that the fresh cells of the yeast-plant breathe like an aquatic animal.
It would seem, then, that the protoplasmic life of animals is identical with that of plants; a certain measure of destructive metamorphosis taking place in each, evolving energy and producing carbon dioxide and water. When, however, this function is examined quantitatively, its maximum is seen to be reached in the animal. While the assimilative function characterizes the plant, the destructive function distinguishes the animal. Hence it is the function of the plant to store up energy to produce the highly complex protoplasm. This, consumed by the animal as his food, continues his existence as a living being, the energy gradually set free by its successive steps of retrogressive metamorphosis appearing as the work which he performs. If this view be correct, it would follow that every individual substance found in the animal—save only those which result from degradation—must be found in the plant upon which it feeds, and this is the fact. The myosine which Kühne has shown to be the distinctive proteid of muscle, Vines has found in the aleuron-grains of the lupine and the castor-oil plant, along with vitelline, the special proteid of the vitellus. The researches of Weyl and Bischoff have proved that gluten is formed in the dough of wheat-flour by the action of a ferment upon the globuline-substance or plant-myosine which it contains, precisely as Hammarsten has shown fibrine is produced in the action of a similar ferment upon fibrinogen. Not only this; Hoppe-Seyler has extracted from maize the identical substance which has been shown by Liebreich to be the essential chemical constituent of nerve-tissue, protagon.
