620 MAN AS A CONQUEROR 



where conditions of famine and war were found. In 1909, the trans- 

 mission of typhus was first correlated with the bite of the body louse 

 or "cootie." During the World War the disease was kept under con- 

 trol through the disinfection not only of wearing apparel but also of 

 the soldiers themselves in "de-lousing" plants which were established 

 back of the front-line trenches. 



Other Diseases Carried by Insects 



Numerous protozoan diseases are carried by insects. In tropical 

 countries, especially, several diseases of cattle as well as of man are 

 caused by trypanosomes, tiny protozoans belonging to the group 

 of the flagellates. One species (7". gamhiense) produces the African 

 sleeping sickness while another form {T. cruzi) causes Chagas' disease 

 in South and Central America. 



Many other diseases of man are caused by parasitic protozoans. 

 Amebic dysentery is caused by the presence of Endameba histolytica, 

 which lives in the colon of the digestive tract. These parasites are 

 much more widely spread than was formerly thought, for even in this 

 country from 5 to 10 per cent of the population carry this parasite. 

 Amebic dysentery received considerable publicity during the recent 

 World's Fair at Chicago when several carriers were discovered 

 handling food and a number of cases were traced to Chicago. Among 

 other ijisect-borne diseases are kola azar, a tropical fever, which 

 is thought to be carried by fleas and bedbugs ; dengue, a disease 

 caused by a filtrable virus carried by mosquitoes ; pappataci, a 

 tropical disease believed to be caused by a filtrable virus and carried 

 by a sand-fly; and possibly poliomyelitis, which is thought to be 

 carried by flies. 



Animals Other Than Insects May Spread Disease 



The arachnids or ticks are serious enemies of higher animals, 

 especially cattle, because they transmit such diseases as Texas fever, 

 and in the case of man, the Rocky Mountain spotted fever. The 

 relapsing fevers of the tropics are also believed to be carried by ticks 

 as well as by bedbugs, fleas, and some biting flies. 



Bubonic plague, the Black Death of the Middle Ages, is estimated 

 to have killed over 25,000,000 people in Europe during the fourteenth 

 century. It even reached this country about 1900, killing more than 

 100 persons in California during the succeeding four years. At pres- 

 ent, there are several endemic foci of the disease, one in China, one 



