SPOROZOA 1117 



that almost half (45 per cent) the infections are latent, give rise 

 to no symptoms and have negative histories. 



6. The carrier state is found among natives or persons long 

 resident in malarial regions, and, aside from the presence of a 

 large spleen and some secondary anemia, may present no symptoms. 

 It is particularly common among native children, tramps and vaga- 

 bonds. It is not uncommon to find fifty to one hundred per cent 

 of the children in a native village harboring the parasite. 



THE DEVELOPMENT OF THE HUMAN MALARIAL PARASITE 

 IN THE MOSQUITO 



(Sexual half of the life cycle, Sporogonie) 



For this stage to be successful the mosquito must bite a malarial 

 patient with gametes in his blood, for if the patient be one in the 

 first stage of the disease, with only schizonts in his blood, no infec- 

 tion of the mosquito will take place, since the schizonts all perish 

 in its stomach. On the contrary, if the mosquito takes blood from 

 a person who has been ill with malaria for some time, or from an 

 apparently healthy carrier, the schizonts die as usual, but the 

 gametes find in the mosquito stomach for the first time conditions 

 suitable for their further development. 



The various stages may be studied by causing suitable species 

 of anophelin.es to bite persons with many gametes in their blood, 

 and then dissecting the stomach and observing the changes which 

 take place there. The development is visible in unstained specimens 

 with high, dry lenses. Since there is no essential difference in the 

 development of the three forms of malaria in the mosquito, they will 

 be considered together. The first stage has already been described 

 in discussing the appearance and behavior of gametes in fresh blood. 

 In the mosquito the process may be followed further; the macro- 

 gamete, freed from its enveloping red cell, projects a little mound 

 on its surface, and this apparently attracts the microgametes to 

 its neighborhood. Into this microphyle one, but never more, of the 

 flagella penetrates, following which the mound is instantly retracted. 

 The fertilized macrogamete, now called a "zygote," soon develops 

 the power of vermicular motion, then being called an ookinet, and 

 travels to the wall of the stomach, and, like the coccodia, penetrates 

 an epithelial cell and there encysts, making the oocyst. This grows 



