314 APPLIED BIOLOGY 



if taken in large doses just as the fever is subsiding, which is 

 while the young spores are free in the blood-plasma. Killing 

 the parasites in human blood prevents infection of mosquitoes; 

 and if all people could be treated with quinine systematically, 

 it is probable that the disease could be stamped out. This 

 has been tried under the direction of Dr. Koch with great 

 success in some small islands. Preventing the spread of the 

 malarial parasite by preventing the breeding of mosquitoes 

 and by protection against bites will be discussed under insects 

 and disease ( 329). In the ten years since it was found that 

 mosquitoes are responsible for the spread of malaria, a great 

 effort has been made to exterminate the insects in many 

 localities, with the result that there has been a decided decrease 

 of malaria wherever the mosquitoes have become rare. Pro- 

 tection against bites by sleeping in screened houses and by 

 wearing mosquito-proof clothing and a veil when outdoors 

 at night has greatly reduced the number of cases of malaria 

 among the employees of certain railroad systems along the 

 Mediterranean shore. 



275. The Parasite of Sleeping Sickness. The terrible 

 South African disease known as the sleeping sickness, from 

 which more than half a million natives in the Congo region 

 have perished in the last ten years, is now known to be due to 

 a parasitic protozoan, which is injected into human blood- 

 plasma by the bite of a peculiar African fly. The parasite 

 swims freely in blood-plasma, its movement being due to long 

 whip-like structures, called flagella. It belongs to a group 

 of Protozoa known as the trypanosomes. Many experts on 

 parasitic diseases are now engaged in studying the sleeping 

 sickness; but so far no satisfactory remedy has been dis- 

 covered. It is spreading rapidly, and has become one of the 

 greatest problems in Africa. 



A similar parasite, injected by a similar fly, causes the 

 disease of horses, mules, and oxen called "nagana" by the 

 natives, and by them correctly charged to the tsetse-fly. 



