238 POPULAR SCIENCE MONTHLY 



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 pro- 

 fessor of zoology at Borne, well known for his researches on the ancestry 

 of insects, on the social communities of tbe white ants and on compara- 

 tive anatomy; these researches on unpractical subjects furnished him 

 with the method for attacking the malarial germ, and for making the 

 marshes around Eome 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 prac- 

 tical 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 infec- 

 tious 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 nat- 

 ural 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. Bemove 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. Bemove the timber from moun- 



