Page:Popular Science Monthly Volume 73.djvu/242

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practical ideas grew out of his theoretical investigations of insects and worms.

Just at the present time the center of interest in medicine is the study of those infectious diseases produced not by bacteria, but by other one-celled germs, the animal protozoa. Among them are the blood parasites that produce malaria, yellow fever, syphilis and the terrible sleeping sickness of Africa, as well as the intestinal parasites of bloody dysentery; another one of them produces the Texas fever of cattle. Many investigators have contributed to our knowledge of these diseases since the time when Laveran discovered the germ of malaria, and prominent among them are the names of Grassi and Schaudinn. Grassi is professor of zoology at Borne, well known for his researches on the ancestry of insects, on the social communities of tbe white ants and on comparative anatomy; these researches on unpractical subjects furnished him with the method for attacking the malarial germ, and for making the marshes around Rome nearly free from that disease. Schaudinn worked at Berlin on the life histories of salt-water protozoa, discovering much of broad theoretical importance, indeed with much greater success than the long line of naturalists before him. He was no physician, he was a biologist, yet he ultimately attained one of the most desired medical chairs in Germany. His genius, and in a measure he is to be compared with Pasteur, lay in his success in unraveling complex life histories; he learned the method in studying the free-living forms, and therefore was enabled to work out the life histories of several that endanger the human body. He never had any direct interest in practical medicine, yet what help his work has brought to medicine! What he did in this direction, the zoologists Leuckart and Leidy did in another by their discoveries on the parasitic worms of man, and on the mode of infection; they all had little thought of practical application. Such biologists have taught pathologists that in the cure of any infectious diseases the first thing to be determined is the life history of the parasite, and this subject is a biological one.

Besides seeking the prevention of disease man has to meet the natural struggle for existence in another way, by securing food, and this means the nurture of his flocks and crops. Here again pure science has proved a valuable pioneer. Naturalists have long since recognized the close dependence of species upon each other, that what affects one comes in the long run to affect all. This is a dependence based upon the struggle for food. Remove one element, as one species, and a more or less general profound disturbance follows. Mankind is in no way exempt from this law. Decimate or extirpate a particular kind of insect-eating bird, and the insects that formed its diet will increase in numbers. Man will feel the disturbance should such insects happen to affect vegetation that is of human use. Remove the timber from moun-