252 THE SPOROZOA 



in breadth. The sporozoites are at first implanted upon the 

 masses of residual protoplasm, representing the remnants of the 

 sporoblasts, but soon free themselves and perform active movements 

 within the cyst. The residual masses are usually enucleate, but 

 sometimes contain residuary nuclei, which may even multiply, 

 though doomed eventually to perish. Ultimately the residual 

 masses derived from different sporoblasts appear to fuse into a 

 smaller number of large granular masses, in which are found also 

 the melanin-granules of the sporont (Fig. 68, XVIII). The whole 

 number of sporozoites formed in this way in an oocyst is very 

 great, but varies within wide limits, from some hundreds to over 

 ten thousand. The mosquito observed by Grassi, of which mention 

 has been made above, might therefore have been capable of dis- 

 seminating about five millions of malarial germs. 



During the whole period of the development of the sporo- 

 zoites, which lasts from ten to twelve days, the oocyst grows 

 continually in size. When the sporogony is complete the cyst 

 bursts, and the sporozoites are set free in thousands in the body- 

 cavity (haemocoele) of the mosquito. Here they are carried along 

 in the circulating blood -fluid, and in some way are attracted 

 towards the salivary glands, which they penetrate, filling the 

 secreting cells. When a mosquito thus infected bites a man, it 

 injects, in its usual fashion, a minute drop of saliva into the 

 puncture made by its proboscis, arid with the drop of saliva a 

 swarm of sporozoites pass down into the blood, each the starting- 

 point of a new infection and of many schizogonous generations. 

 Thus the life-cycle of the parasite has been brought round again 

 to the point which was selected for commencing the description. 



From the above account it is seen that the life-cycle of the malarial 

 parasite is now thoroughly known in all its features. There is, however, 

 one point of importance still to be made out. In patients apparently 

 cured of malaria it may appear again without a fresh infection, and it is 

 not known what has been the condition of the parasite in the period 

 intervening between the first attack and the relapse. In cases of chronic 

 malarial cachexy, only crescents are to be found in the blood, and Grassi 

 has suggested that the gametocytes may have the power of non- sexual 

 reproduction in such cases, their offspring causing a reinfection of the 

 host. This point has recently been investigated by Schaudinn [94] in 

 the case of the tertian parasite, and he finds that such cases of relapse 

 are brought about by a sort of parthenogenetic reproduction on the part 

 of the resistent, long-lived macrogametocytes. The nucleus of a macro- 

 gametocyte becomes slightly drawn out and shows at one extremity a 

 number of deeply-staining, coarse grains of chromatin ; it then divides 

 into two, so that the gametocyte contains two nuclei, one rich in chromatin 

 and staining deeply, the other pale and staining feebly. The body of 

 the gametocyte may become partially constricted into two parts, one with 



