132 LIFE-CYCLE OF MALARIAL PARASITE [CH. 



At this stage there are now three types ol parasites, viz. 

 the schizonts, macrogametocytes and microgametocytes, the 

 two latter belonging to the sexual and the former to the asexual 

 cycle. 



The sexual cycle cannot be completed in the blood but 

 only in the internal organs of those species of mosquito which 

 transmit the infection. In the absence of these the micro- 

 gametocytes soon die off without any further development 

 taking place. 



The macrogametocytes, on the other hand, are much more 

 resistant, and can remain in the body for very considerable 

 periods. These are the forms that are supposed to be respon- 

 sible for the cases of latent malaria, in which a patient may 

 remain in good health for some years and then suddenly develop 

 typical malaria without having been exposed to the possibility 

 of re-infection. In these cases it is the macrogametocytes that 

 have remained dormant in the body waiting for a convenient 

 opportunity to develop, such as that afforded by a chill or any 

 other diminution in the vitality of the patient. Under these 

 circumstances the macrogametocyte develops parthenogeneti- 

 cally. Its nucleus divides into two parts, one densely chromatic 

 and the other poor in chromatin. The pigment granules and 

 other waste products gather round the latter, and the whole 

 is divided off from the remaining protoplasm and constitutes 

 a sort of residuum similar to that left behind by th'=> merozoites. 

 Th-^ remaining part of the macrogametocyte, now much 

 clearer by the loss of its pigment granules, divides up into a 

 number of merozoites in exactly the same way as an ordinary 

 schizont, and the merozoites escaping into the blood plasma 

 penetrate other red cells and thus start another cycle of 

 schizogony. 



Sexual cycle. — Sporogony. As mentioned above the macro- 

 and microgametocytes only complete their de\'elopment 

 in the internal organs of the mosquito that is responsible 

 for their transmission. When such a mosquito — in the 

 case of malaria only Anophelines — feeds on the blood of 

 a patient containing sexual forms, in addition to the 

 latter, it ingests many parasites belonging to the schizogonous 



