MALARIA AND ITS TRANSMISSION 27 



being reached in forty-eight or seventy-two hours, 

 according to the variety of the parasite. At the 

 termination of growth sporulation occurs, and the 

 paroxysm takes place, corresponding to the liberation 

 of the new generation of parasites (merozoites) in the 

 blood plasma. Again the red corpuscles are attacked 

 and the asexual round continues. 



The malaria pigmented spleen and liver give evidence 

 of the enormous activities of the leucocytes in captur- 

 ing the parasites as they are set free in the blood plasma. 



Time Factor. — Although there are some localities 

 in which the inhabitants are all infected with malaria, 

 newcomers or visitors may or may not soon fall a prey 

 to the disease, for the reason that not more than 25 

 to 35 P er cent °f tne Anopheles mosquitoes are in- 

 fected during the height of the season, and correspond- 

 ingly less early in the spring. This is dependent upon 

 both the time when the infected person and the next 

 victim are bitten. Obviously the mosquito cannot 

 transmit malaria when there is none present to be 

 transmitted ; again, the sexual parasites (gametes) 

 must be in the peripheral circulation when the mosquito 

 bites the infected individual ; and again after the mos- 

 quito becomes infected a period of not less than six 

 days (possibly five in benign tertian, and twelve days 

 in a_\stivo-autumnal) must elapse before a new victim 

 can be inoculated, i.e. the time required for sexual 

 development of the parasite. This incubation period 

 may be prolonged through reduced temperature, with 



