156 MALARIA 



process of asexual multiplication in the human blood corpuscles 

 begins over again. Since it takes ten or 12 days for the sexual 

 cycle to be completed in the case of astivo-autumnal malaria, 

 an infected mosquito is not dangerous for at least this length of 

 time after biting a malarial patient. However, once the new- 

 generation of spores has been developed, the mosquito remains 

 dangerous for several weeks and may infect many persons, as not 

 all the parasites are poured out of the salivary glands at one 

 biting. 



It is commonly beUeved that malaria parasites not only do not 

 develop but cannot live in the mosquito at a temperature below 

 60° F. but Dr. King has recently shown that the tertian parasite, 

 Plasmodium vivax, can survive several days in Anopheles quadri- 

 maculaius at temperatures slightly below freezing, and can with- 

 stand a mean temperature of 46° F. for 17 days. The sestivo- 

 autumnal parasite, P. falciparum, though more closely confined 

 to the tropics than the other species, was found to survive a 

 temperature of 35° F. for 24 hours. This clearly shows that the 

 malaria parasites can readily pass the winter in the mosquito 

 hosts even in places where the mean temperature may fall con- 

 siderably below 60° F. for some time. 



Other Species. — The other species of malarial parasites dif- 

 fer only in minor details of their structure and development. 

 The tertian parasite, Plasmodium vivax, during the early stages 

 of its development in the blood corpuscles is extremely active. 

 Its unceasing restless changing of shape is fascinating to watch 

 under the microscope and one feels that it was very appro- 

 priately named " vivax." Unlike the malignant parasites of 

 ffistivo-autumnal malaria, the tertian parasites do not tend to 

 clump together, and so do not become plugged in the capillaries 

 but remain constantly in the circulation. To this fact, as will 

 be shown later, is due the " benign " nature of this and also of 

 the quartan parasite. The tertian parasites have the peculiarity 

 of growing very large and of causing the corpuscles which they 

 parasitize to enlarge and become unhealthy in appearance. 

 The number of spores which result from the sporulation every 

 48 hours ranges from ten to 25. According to Ross the normal 

 number of splits of the nucleus is four, which would result in 

 16 spores. One of the most striking points of difference from 

 the " malignant " parasites is the fact that the gametocytes 



