IX] LIFE-CYCLE 159 



commonly gathered at the periphery of the parasite. In contra- 

 distinction to the granules of the other species of malarial 

 parasites, those of P. malarice are non-motile. A vacuole 

 is formed, but is comparatively small and disappears during 

 the growth of the trophozoite. The presence of the parasite 

 in the red cell does not produce any evident changes in the cor- 

 puscle beyond a slight decrease in size and a darker colour. 

 The trophozoite takes about 60 hours to grow up into the 

 mature schizont, which is a somewhat angular body 6-7 /x- in 

 diameter. 



During the next 12 hours the nucleus of the schizont 

 divides up into 6-12 smaller ones, which become arranged 

 in a single circle at the periphery. Each becomes surrounded 

 by a mass of cytoplasm which separates off from its neighbours 

 and thus a regular circle of 6-12 merozoites is formed. The 

 pigment granules form a dark clump at the centre and as the 

 merozoites radiate from it, a very typical rosette appearance 

 is produced. 



The merozoites (about i'75^ m diameter) are now set free 

 by the rupture of the corpuscle and may enter another red cell 

 and repeat the cycle. More often, however, they seem to be 

 killed off by the phagocytes, and thus it is only rarely that this 

 parasite produces fatal effects in its host. 



The whole of the above cycle takes place in the peripheral 

 blood, and occupies 72 hours. 



Accordingly the fever which is caused by this parasite 

 occurs every fourth day (hence the name Quartan Fever) 

 after the schizogony takes place. 



In addition to the simple quartan fever in which the attacks 

 recur every fourth day, cases of double and triple quartan are 

 ^Iso met with. In double quartan fever the attacks recur 

 on the first, second, fourth, fifth, seventh, eighth days, etc. 

 This is merely a case of a double infection, and the parasites 

 being the descendants of two separate lots of sporozoites, are 

 at different stages of development. The first infection will 

 undergo schizogony on the fourth, seventh, tenth days, etc. 

 after the entry of the sporozoites, whilst if the second infection 

 occurs on the day following any of these attacks the latter 



