IOO 



Mosquitoes 



Clinical observation has established for malarial 

 parasites a latent phase of existence ; concurrently 

 with the subsidence of acute symptoms they may 

 disappear from the peripheral circulation. This takes 

 place sometimes spontaneously, but generally by the 



Fig. 21. — Eggs, top views: a, Anopheles crucians; b, A. punc- 

 tipennis; c, A. macidipennis; d, lower side, A. macuhpennis (same 

 scale as Plates vi to vm). 



use of quinine. This vanishing is not permanent, for 

 in the course of weeks or months they reappear in 

 the general circulation simultaneously with a renewal 

 of clinical phenomena. As to the particular organs 

 or tissues in which they return, or as to their morph- 

 ology and histology during latency, we know nothing 

 definite, nor are we better informed as to the condi- 

 tions which cause them to assume active, propagating, 

 circulating existence. We do know that any and all 

 agents that lower physiological resistance in their 

 host tend to bring about conditions which break up, 



