This subject, however interesting, we must reluctantly forsake, referring to the article on NUTRITION, and to the consideration of what has been called the or plastic power in our article on FETAL DEVELOPMENT.
Vegetables and animals, from this review, appear to differ little from one another in all that regards their nutrition. The processes that lead to this conclusion may be, and, indeed, are more complicated among animals than among vegetables ; but the essence of the final act is very nearly the same in both. Neither shall we be able to demonstrate any great want of uniformity between these different classes of organized beings in several of the actions which we shall next discuss ; in others, however, we shall discover an impassable line of demarcation between them. The first of these actions which we shall consider is have already had occasion to mention the watery exhalation and oxygen thrown off by the leaves of vegetables. Divers other substances are excreted by the same parts, —water, various acrid, glutinous, saccharine, and balsamic substances. It is even by means of the leaves that vegetables throw out those substances which they may have absorbed by their roots, and which seemed calculated to injure them. We are at no loss, moreover, to demonstrate numerous apparently glandular Organs in vegetables for the elaboration of a variety of substances, many of them very acrid. The flowers of vegetables secrete, in the first place, certain matters, the infinite variety of whose odours proclaims them to be different; the sectaries are also filled with fluids, which are sweet in many tribes. Lastly, in the flowers, the male fecundating matter, and the fluid that moistens the pistillum are secreted. Nor are vegetables without internal secretions, among the number of which certain aeriform fluids are riot the least curious. The other secretions of vegetables are of infinite variety, —gummy, oleaginous, balsamic, camphoric, &c. &c. These are all stored up in cells con tained in different parts of each individual plant, and undoubtedly either subserve im portant purposes in their several economies, with the nature of which we are very imper fectly acquainted, or are in relation with some other system in the universe, affording food to numerous tribes of insects, or materials which stand in relation to animals and man as means of accomplishing a variety of ends, the impulses to which they bring into the world with them, though they are launched upon existence un furnished with the materials.
We have also hinted at the watery and gazeous products of the respiration of animals, and consideration for a moment enables us to make a long catalogue of other secretions both with reference to individuals and to species. We have, for instance, the limpid
fluids that bedew the cellular and serous mem branes, serum and synovia, and fill various cavities in the body—the chambers of the ear and of the eye particularly ; those that moisten and defend the surfaces of the mucous membranes, the tears and mucus ; those that are subservient to digestion, the saliva, gastric juice, pancreatic juice, and bile ; those that lubricate and prevent the surfaces exposed to the air from drying, the sebaceous or oleaginous fluids of the skin, and cerumen of the ears ; those that are laid up as reservoirs of nutriment or defences from the cold, the fat, marrow, &c.; those that are the vehicles for the worn-out particles of the body, the urine and perspira tion ; those that minister to the reproduction of the species, the fluids of the female germ or ovum, the spermatic and prostatic fluids of the male ; and finally, those that are poured out among the mammalia as the first aliment for the newly-born being, the milk. Nor is the list exhausted, for numerous species of animals have peculiar fluids which are useful to them in the places they hold in the system of creation ; among these are the venomous fluids of serpents, and of the stings of numerous insects, the inky fluid of the cuttle fish, the fetid fluids of the anal glands of the carnivora, rodentia, &c.; the fluid with which spiders weave their web ; the wax with which bees build their cells, &c. Secretion is, therefore, a much more extensive function among animals than among vegetables ; the products are still more various, and the apparatus by which they are eliminated is, generally speaking, far more complicated among the former than among the latter. Certainly, in the very lowest tribes of animals, secretion is an exceedingly simple process contrasted with what it becomes in the higher, whose organization is more complex. Among the polypi, medusx, and entozoa, the whole of this function seems to consist in a kind of transudation, or exhalation from the surface of their homogeneous bodies, without the intermedium of any special organ. Among animals higher in the scale we find secretion performed in two modes,--by vessels, when the act is entitled exhalation, and by means of certain special organs named glands, an arrangement which we also find among vege tables. The skin and pulmonary surface are the great implements of exhalation among animals, as the leaves are among vegetables ; almost all the rest of the secretions take place by the instrumentality of glands.