DISEASES CAUSED BY PROTOZOA. 
121 
The Spirochete of Relapsing Fever. 
The cause of relapsing fever is a group of spiro¬ 
chetes, the individual members of which differ in minor 
details in the various countries where the disease pre¬ 
vails. The spirochetes are long, delicate, threads with 
four to ten spirals and an undulating membrane which 
Fig. 18.—The tsetse fly. 
propels them about actively. They can be found in 
the blood of those sick with the fever by dark field ex¬ 
amination or in stained smears. At present the infec¬ 
tion is most widespread in India and Africa, but sixty 
to seventy years ago epidemics occurred in this country. 
People infected with spirochetes develop a fever of 
relapsing type. First there is a period of fever lasting 
from five to seven days, then a period of remission of 
the same duration. It is spread by the bites of lice and 
ticks which become infected by sucking the blood of 
