402 ELEMENTARY ZOOLOGY. 



cheaper mineral oils. Bristles, brushes, perfumes, oils, 

 glue, buttons, and fertilizers are only a portion of the 

 numerous by-products of the modern meat-packing 

 houses. Ornaments are made of teeth, of corals, and of 

 pearls. Many animals are scavengers, attacking and 

 destroying carrion and other decaying organic matter. 



402. Animals Directly Injurious to Man. When man 

 first appeared on the earth many mammals now extinct, 

 much larger and fiercer than those of the present time, 

 were abundant. Unquestionably these were much more 

 of a menace to him then than the predaceous animals are 

 now. These animals, except in a few poorly inhabited 

 parts of the world, are now practically negligible. A few 

 poisonous snakes, some sharks and crocodiles, a few 

 members of the cat family, and a few species of bear, 

 almost extinct, about exhaust the list of animals really 

 dangerous because of size or ferocity. But in place of 

 these there are now numerous species that are no less 

 dangerous to him because of diseases which they bring to 

 man directly or indirectly. Reference has been made 

 to the Protozoa which produce malaria and yellow fever, 

 and to the intestinal and other parasites that belong to 

 the unsegmented worms and produce all sorts of discom- 

 fort, inefficiency, and disease among men. The mosquitos 

 and flies and other insects that spread these diseases are 

 just as important to us as the germs themselves. The 

 bubonic plague is believed to be a disease of rats and 

 other rodents carried to man from the rat by fleas. All 

 these temporary external parasites that go from animal 

 to animal, as lice, fleas, bed-bugs, mosquitoes, etc., are 

 especially favorably situated to be the carrier of disease. 

 Cattle are subject to tuberculosis ; and many investigators 



