194 



Arthropods as Hosts of Pathogenic Protozoa 



J^^^^ 



proof hut. Though they took no quinine and all of their neighbors 

 suffered from malaria, they were absolutely free from the disease. 

 To complete the proof, mosquitoes which had fed in Rome on 

 malarious patients were sent to England and allowed to bite two 

 volunteers, one of them Dr. Manson's own son, who had not been 

 otherwise exposed to the disease. Both of these gentlemen con- 

 tracted typical cases of malaria and the parasites were to be found in 

 abundance in their blood. 



Since that time there have been many practical demonstrations 

 of the fact that malaria is transmitted exclusively by the bite of 



mosquitoes and that the destruc- 

 tion of the mosquitoes means the 

 elimination of the disease. 



We have said that the malarial 

 parasite is able to undergo its 

 development only in certain 

 species of mosquitoes belonging 

 to the Anopheline group. It is 

 by no means certain that all of 

 this group even, are capable of 

 acting as the definitive host of 

 the parasites, and much careful 

 experiment work is still needed 

 along this line. In the United 

 States, several species have been 



127. Eggs of Anopheles. After Howard. foUud tO be implicated, ^MO^efe^ 



quadrimaculatus and Anopheles 

 crucians being the most common. The characteristics of these species 

 and the distinctions between them and other mosquitoes will be 

 discussed in Chapter XII. 



In antimalarial work it is desirable to distinguish the anopheline 

 mosquitoes from the culicine species in all stages. The following 

 tabulation presents the more striking distinctions between the groups 

 as represented in the United States. 



Anopheles 

 Eggs: Laid singly in small 

 numbers upon the surface of the 

 water. Eggs lie upon their sides 

 and float by means of lateral 

 expansions (fig. 127). 



Culex, Aedes, etc. 

 Deposited in clumps in the 

 form of a raft (Culex group) or 

 deposited singly in the water or 

 on the ground in places which 

 may later be submerged. 



