33 2 MANUAL OF BACTERIOLOGY. 



The extra-cellular forms of the parasite (gametes), incapable of fur- 

 ther development in their human intermediate host, can continue their 

 life cycle only when, by chance, they happen to be sucked into the body of 

 a mosquito of the genus Anopheles (definite host), in which they un- 

 dergo a second complete (sexual) cycle of development with the ultimate 

 production of spores (sporozoids). When in turn the spores chance to 

 be inoculated into the blood of man by the bite of an infected Anopheles, 

 the man becomes infected, and the cycle of development in the red 

 corpuscle, already outlined, commences. The second or sexual cycle of 

 the parasite in the mosquito, here described for the tertian organism, 

 applies as well to the other varieties of the malarial organism, namely 

 the quartan and the aestivo-autumnal forms, in the case of each starting 

 from the extra-cellular mature forms of the organism found in the 

 blood of the human host. 1 



Quartan Parasite. This resembles quite closely the ter- 

 tian parasite, but differs from it in certain respects. The 

 young, hyaline, intra-corpuscular parasite is more highly 

 refractive, its amoeboid motion is less marked and more 

 sluggish, and the pigment granules are darker, much coarser, 

 and have very slight motility. The infected red corpuscles 

 are usually somewhat contracted instead of swollen and 

 their color is apt to be darker, assuming a bronzed hue. The 

 full-grown parasite is much smaller than the corresponding 

 form of the tertian, approximating the size of a normal red 

 corpuscle. As segmentation begins, a characteristic appear- 

 ance develops which distinguishes the quartan organism, 

 namely, the coarse pigment granules are drawn toward the 

 center of the parasite in certain converging straight paths, 

 giving a stellate arrangement to the pigment, until finally it 

 becomes clumped entirely at the center in a solid mass. The 

 segmenting forms of the quartan parasite thus present a 

 more symmetrical arrangement of the spores, which often 

 resemble the petals of a " marguerite." These spores are 

 oval and number only from six to twelve, being fewer than 

 those of the tertian segmenting parasite. The quartan 



1 Lyon, "The Inoculation of Malaria by the Mosquito: A Review of 

 the Literature," Medical Record, February 17, 1900. 



