Page:Popular Science Monthly Volume 23.djvu/832

This page has been proofread, but needs to be validated.

and Animal Life," at least two important contributions to the same subject have made their appearance. One of these, written by Mr. P. Geddes, of Edinburgh, may be found in "Nature" of January 26, 1882. The other, from the pen of Professor E. Ray Lankester, was published in the April number of the "Quarterly Journal of Microscopical Science."

The spectroscopic examination of animal pigments, a line of investigation in which Professor Lankester was one of the earliest observers, has shed much light on these previously little known compounds, and has opened a wide field for further research. Especially fruitful in this direction was the announcement, perhaps a dozen years ago, that various animal greens yield a spectrum identical or nearly so with that furnished by chlorophyl, the common green coloring-matter of plants. At once a host of interesting questions sprang up as to the occurrence structure, and properties of "animal chlorophyl"—all of which, however, culminated in this: Is the color "accidental" and unimportant in animals, or has it rather some profound significance, such as attaches to it when it is found in vegetable protoplasm?

It may well be considered as one of the fundamental truths of biology that chlorophyl in vegetable substance is no insignificant intruder. Though the exact method of its working is just now a matter of much dispute, the broad fact of its usefulness is freely admitted; in one way or in another, chlorophyl aids in the economy of the vegetable cell so that it feeds greedily upon the carbonic acid of the surrounding air or water, and tears to pieces, for building up afresh its own substance, compounds which, without chlorophyl, it would be powerless to utilize, or which if utilized would be speedily sacrificed. A long series of experiments, reaching from the time of Priestley to the present day, uphold and strengthen this fundamental fact; but, among them all, the simplest is the most unique and the most pronounced. If a piece of a green plant be immersed in water and exposed to sunlight, bubbles of oxygen are given off, and analysis will prove that carbonic acid has simultaneously disappeared from the water. With plants not green, or with animals, the facts are reversed—oxygen disappears and is replaced by carbonic acid.

The green plants, then, exhibit a peculiar power, viz., that of splitting up carbonic acid, and of availing themselves for the manufacture of starch, etc., of the carbon thus gained; at the same time procuring such a large supply of oxygen that they are able to reject a vast amount over and above their own needs. In this respect they differ from colorless plants and animals, and for this power they depend exclusively upon the agency of chlorophyl. We have no evidence whatever that the chlorophyl of plants has ordinarily any other function.

Very considerable interest has consequently been felt in the solution of the question, What significance (if any) has chlorophyl when found in animals? And since the only known use to which it could