DISEASES CAUSED BY PROTOZOA. 
125 
on the water the larvae cannot hatch out into mos¬ 
quitoes. Swamps, when it is practical to do so, should 
be drained or filled in. In districts where malaria is 
known to exist, the house should be screened. 
Trypanosomes. 
A trypanosome is a long micro-organism with 
spirally twisted body. On one side is a membrane the 
edge of which is cord-like and extends beyond the body 
to form a whip or flagellum. The wave-like move¬ 
ments of the membrane and the movements of the 
flagellum propel the trypanosome about. The proto¬ 
plasm is granular and contains two nuclei. Reproduc¬ 
tion takes place by a longitudinal splitting of the 
whole cell body. The life cycle is not clear, but in 
some species at least there is development in an inter¬ 
mediate host, generally some species of fly. 
There are about 60 species of trypanosomes, many 
of which are pathogenic for animals but only two are 
known to cause disease in man. The Trypanosoma 
gambiense is the cause of the Sleeping Sickness, a dis¬ 
ease prevalent in equatorial Africa. 
One of the natural hosts of the parasite is the 
crocodile and a species of fly, the Glossura palpales, 
that feeds on the blood of these animals and transmits 
the infection to human beings. Trypanosomiasis or 
the sleeping sickness, is a chronic disorder marked by 
fever, wasting and lethargy. The parasites can be 
found in the blood but more often in the cerebrospinal 
fluid. No way of establishing immunity is known. 
