IX] LIFE-CYCLE l6l 



malaria by their active amoeboid movements. The tropho- 

 zoites grow rapidly and assume an oval form ; they contain a few 

 pigment granules which are small, irregular and only feebly 

 motile. During its growth the parasite causes an alteration 

 in the substance of the red cell, which in stained preparations 

 is seen to contain a number of granules known as Maurer's 

 dots. Otherwise the erythrocyte remains unaltered in ap- 

 pearance until the formation of the merozoites results in its 

 destruction. 



The fully developed schizont is 4*5 to 5/x in diameter, and is 

 very rarely present in the peripheral circulation. It segments 

 into 8-10 or sometimes 15 merozoites, which may either be 

 arranged in the form of a rosette, or irregularly. The segmenta- 

 tion almost invariably takes place in the capillaries of the 

 internal organs, and when it is in process there is a tendency 

 for the red cells to cling together and also adhere to the wall of 

 the blood-vessel, thus causing obstruction of the circulation. 



The whole cycle of schizogony takes from 24 to 48 hours 

 to be completed, and thus the febrile attacks are more or less 

 irregular, but often occur each day. 



The gametocytes develop from the trophozoites in the usual 

 manner, but are distinguished from those of the other two 

 human species of Plasmodium by their crescentic form. The 

 macrogametocyte may be distinguished by the arrangement 

 of the pigment, which is usually concentrated in the neighbour- 

 hood of the compact nucleus, leaving the remainder of the 

 cytoplasm clear. In the microgametocyte the pigment is 

 irregularly scattered through the cytoplasm and the nucleus 

 is somewhat diffuse. Moreover the shape of the two kinds of 

 gametocytes is different, being long and thin in the case of the 

 former, and broad and somewhat rounded in the latter. The 

 remains of the distorted red cell may be seen surrounding the 

 " crescents," the haemoglobin often being concentrated in the 

 form of a small clump attached to the side of the parasite. The 

 dimensions of a fully grown macrogametocyte are about 

 12. < X 4-.. 



These gametocytes are very conspicuous in the circulation 

 of patients suffering from P. falciparum, and under the name of 



H. B. F. n 



