MALARIA AND ITS TRANSMISSION 25 



way out of the human body, and in this connection 

 it is interesting to note that the early phases of the 

 sexual cycle may be undergone on a glass slide, in 

 a blood smear, but owing to temperature conditions 

 and most particularly lack of proper chemical con- 

 ditions, the organisms die in a few minutes. Any 

 blood-sucking insect or mechanical means of drawing 

 blood may produce the same result ; but if this blood, 

 however much parasitized it may be, is swallowed by 

 any other insect than the Anopheline mosquito, both 

 blood and parasites are digested as food. But in the 

 Anopheline mosquito the sexual cycle is completed ; 

 therefore this insect is the definitive host. 



In the asexual stage there are present the gametes 

 (sexual parasites) which are distinguishable from the 

 asexual forms by "(1) their larger size, (2) by more 

 abundant pigment, (3) by the fact that there is only 

 one fairly large chromatin mass, whereas in an asexual 

 form of nearly equal size the chromatin has already 

 begun to divide into several portions (presegmenting 

 stage)." * The aestivo-autumnal gametes (crescents) 

 have already been described. 



If, now, a malarial patient with gametes (sexual 

 parasites) present in the peripheral circulation is bitten 

 by an Anopheline mosquito, the conditions are right 

 for the completion of the sexual cycle in that in- 

 sect (Fig. 4, 9-20). The male gametocyte undergoes 



1 Stephens and Christophers. " Practical Study of Malaria." Liverpool 

 Univ. Press, 1908. 



