130 



THE ANIMALS AND MAN 



serious diseases are caused by Protozoan germs. The 

 terrible sleeping sickness of Africa is one of these and, as 

 with malaria, the germs are spread from man to man by a 

 .blood-sucking insect. This is not the mosquito but a 

 larger heavier fly called the tse-tse, which is rather like a 

 small horse-fly in general appearance. 



Yellow fever is also almost certainly caused by a Protozoan 



parasite, which is 

 distributed exclu- 

 sively by mosqui- 

 toes. Several infec- 

 t i o u s diseases of 

 domestic animals 

 are caused by Pro- 

 tozoa. The best 

 known of these in 

 this country is the 

 Texas or splenic 

 cattle fever, the 

 germs of which pass 

 part of their life in 

 the bodies of ticks 



FIG. 52. Texas fever tick, Mar gar opus an- and are distributed 

 nulatus; young adult not fully gorged. , them frQm ^ { _ 

 (After Doane.) ' . 



mal to animal. 



These germs, called Piroplasma, have the interesting power 

 of entering the eggs in the body of the female tick so that 

 when the young ticks hatch from these eggs, which are laid 

 on the ground when the old ticks drop off from the cattle 

 upon which they have been holding while sucking 

 their blood, these young ticks are already inoculated 

 with germs. When cattle are attacked by these young 

 ticks they become inoculated with the fever by the escape 

 of the germs from the bodies of the ticks into their blood. 

 The characteristic common to all these Protozoa-caused 



