middle intestine (stomach) of the mosquito in which it had developed. Here it comes to rest and is soon surrounded with a capsule. It is now an oöcyst. Presently it divides into a number of daughter cells and residual bodies. The former produce a vast number as many as ten thousand in a single oöcyst of minute bodies, the sporozoites (zygotoblasts, germinal rods Ross). Finally the oöcyst ruptures, discharging the sporozoites into the body cavity of the insect, whence they are transferred to the salivary glands, in the secretion of which, opportunity offering, they are injected into the blood of an appropriate vertebrate, whose blood corpuscles they subsequently enter, and, becoming schizonts, renew the cycle. The process of multiplication in this the sexual or exogenous cycle is called sporogony.
Latent phase. It is a well-established fact that, concurrently with the subsidence of acute clinical symptoms, the malaria parasite may disappear from the general circulation. This it does either spontaneously or as a result of the administration of quinine. In the majority of instances the disappearance is only temporary. Usually, after an interval of weeks or months, the parasite reappears in the general circulation and there is a renewal of the clinical phenomena. As to the organ or tissue it selects, or as to its appearance and structure during this time of latency, or as to the exact conditions which cause it once more to resume active, propagating, circulating life, nothing is positively known.
Three opinions, each of them founded on a certain amount of fact, have been advanced on this point: (a) That the parasites, when the conditions become unfavourable for schizogony, become encysted and lay up in the spleen or other organ, (b) That they never completely leave the circulation, but continue to propagate in the usual way, though in numbers so small that it is practically impossible to find them even by prolonged microscopical examination, (c) That certain sexual forms (macrogametes), a phase of the parasite apt to persist for prolonged periods in the blood, forms parthenogenetically and while still in
