THEIR RELATION TO MAN 207 



are both needful to the continued existence of the 

 disease. 



There are other tropical fevers that are probably as 

 much dependent upon other mosquitoes, but we know 

 less about them. We do know that several forms of 

 bird malaria, due to species of Proteosoma, are also de- 

 pendent upon mosquitoes as intermediate hosts, and 



FIG. 96. The Tsetse-fly, Glossina morsitans. 



how many diseases of other animals are transmitted by 

 them is as yet matter of conjecture only. 



A species of Culex very closely allied to our common 

 "house" or " rain -barrel " pest is responsible for the 

 transmission of that tropical disease "filariasis" which 

 sometimes causes the abnormal enlargement of the 

 lymphatics and thickening of the skin, known as "ele- 

 phantiasis." Other species have been charged with 

 being agents in the transmission of leprosy, but this 

 must be considered "not proven" as yet. 



In all these cases, the mosquito is an intermediate 

 host: not a mere carrier, but a fellow sufferer with 

 man, subject to another form of the same disease, 



