Page:Popular Science Monthly Volume 21.djvu/854

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Thus the green bodies of animals do not correspond with the chlorophyl-bodies of the algæ, but are independent organisms, or one-celled algæ, which have been named zoöchlorella. Yellow cells are found living under similar relations in actinias and radiolarias, which have been distinguished as zoöxanthella.

The physiological as well as morphological independence of the green cells is also demonstrated by the fact that when separated from the animals they continued to live in this condition for days and weeks, and formed starch in the sunlight. When grafted upon hydras and infusoriæ, which were quite free from chlorophyl, they continued to live upon them.

The conclusion is drawn from these researches that self-formed chlorophyl is wanting in real animals, and that, when it is present in their bodies, it originates in plants that have immigrated to them. The most interesting result from them is the answer they give to the question as to the significance of the green and yellow algæ to the animals in which they occur. In order to examine this matter more closely, colonies of radiolarii containing numerous yellow cells were put into filtered sea-water. They not only continued to live in it, but outlived the specimens that were left with the other organisms. Now, since the radiolarii are real animals, incapable of living on any but organic matter, while in this case air and water afforded them all the support they required, they could have been kept alive only by the yellow cells that lived upon them, working up the inorganic substances that were provided for them, under the influence of light, into organic. Further experiments showed that fresh-water sponges could be cultivated to the best advantage in filtered water, thus demonstrating that the zoöchlorella and the zoöxanthella are fully competent to maintain the animals in which they live. If the animals contain few or no green or yellow algæ, they are fed, like real animals, by the assimilation of solid organic matter; but, when they contain algæ, they may be fed, like real plants, by the assimilation of inorganic matter. In the latter case, the algæ living in animals perform precisely the same function as the chlorophyl-bodies of plants.


PROFESSOR RUDOLF VIRCHOW is almost equally well known as the leader of one of the principal German schools of scientific thought and as a prominent actor in the field of German politics. In the former capacity his name is inseparably associated with the theory of cellular pathology, which he first expounded and which he has maintained with eminent consistency; in the latter character he has gained an honorable fame as a faithful guardian of the municipal in-