Page:Popular Science Monthly Volume 23.djvu/833

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in general be put (inferring from plants) is in decomposing carbonic acid, and thus aiding alimentation, it has become an important question to discover if this same physiological habit belongs to animal chlorophyl. If it can be proved that animal substance endowed with chlorophyl can, just as well as plant protoplasm similarly colored, break down carbonic acid and utilize its elements, then we remove the last formidable barrier between plant and animal protoplasm. If it should be shown, on the other hand, that when found in animals it is always functionally incapable of splitting up carbonic acid, it is true that we preserve a point of difference between plants and animals, but a result so negative would land us in a new difficulty, viz., that of explaining its presence by attributing to it some other function, and one unknown to plant chlorophyl. No sufficient explanation of this kind has hitherto been offered. In some cases a "protective resemblance" to vegetation would explain its occurrence; but in most cases this is out of the question.

Now, up to 1878 no evidence of value had ever been advanced to show that animal chlorophyl does enable its host to split up carbonic acid and give off the excess of oxygen resulting. In that year, however, Mr. Geddes, whose later work is referred to above, visited Roscoff and found there quantities of "the grass-green planarian (worm) Convoluta Schultzii, of which multitudes are to be found in certain localities on the coast, lying on the sand covered only by an inch or two of water, and apparently basking in the sun. It was only necessary to expose a quantity of these animals to direct sunlight to observe the rapid evolution of bubbles of gas, which, when collected and analyzed, yielded from forty-five to fifty-five per cent of oxygen."

Having obtained so much of valuable evidence, Mr. Geddes followed up his discovery by examining these green worms to see whether or not the animal protoplasm derives the same kind of benefit from its work as does plant protoplasm which is known, as a result of the co-operation of chlorophyl, to build up starch or starchy compounds.

This, indeed, proved to be the case, for he adds: "Both chemical and histological observations showed the abundant presence of starch in the green cells; and thus these planarians, and presumably also Hydra, Spongilla, etc., were proved to be truly 'vegetating animals.'"

The only link here needed is the full proof that the "grass-green planarian" owed his color to veritable chlorophyl. There is little or no reason to doubt it; yet, when we are told by Professor Lankester that in Spongilla alone among animals has spectroscopic investigation really proved the presence of that pigment, we can not help wishing that this confirmatory evidence had been obtained by Mr. Geddes.

Meantime slow progress had been making in a kindred subject. Before speaking of this, however, it must be said that chlorophyl is now known to be by no means a simple substance, but is rather made