88 



TROPICAL MEDICINE AND HYGIENE 



a considerable proportion of the inhabitants. On the 

 Upper Shire River and the south end of Lake Nyassa, as 

 well as on the plateaux, elephantiasis amongst the indi- 

 genous inhabitants is unknown, and ftlariae are extremely 

 rare. 



In British Guiana these embryos are very frequently 

 found in the blood of persons living on the coast, but are 

 not found in persons living in the interior, and no cases of 

 elephantiasis come from the interior. 



FIG. 41. Showing the incidence of filaria and elephantiasis 



in different races in British Guiana. Percentage with 



elephantiasis. Percentage with filaria. 



In a community formed by the association of persons 

 of several races, and living under the same meteorological 

 conditions, it will often be found that the incidence of 

 elephantiasis varies in these different races, and when this 

 occurs there is the same variation in the prevalence of 

 filariasis. For example, in the towns of British Guiana 

 there are Portuguese, Negroes and Indians, and the pro- 

 portion in the males of each race with filanae was 30 : 18 : 4. 



