128 LIFE-CYCLE OF MALARIAL PARASITE [CH. 



cytoplasm becomes spread out and exhibits a characteristic, 

 comparatively large, clear, central vacuole, the effect of which 

 is to give the parasite the appearance of a ring, such ring 

 forms occurring in the early stages of development of all three 

 forms of the parasite. In fresh preparations these ring forms 

 can be seen to possess on one part of their circumference a 

 swelling like the stone of a signet ring which is the nucleus, 

 and to extrude small pseudopodial processes, which in some 

 forms are very long and slender, in others more lobose. In 

 specimens stained by the Romanowsky method the nuclear 

 portion is conspicuous as a bright red mass, whilst lying around 

 the vacuole is a thin crescentic portion of delicate blue-staining 

 cytoplasm. 



Many of the ring forms, especially in the case of the malig- 

 nant tertian parasite, remain for some time attached to the 

 surface of the red blood corpuscle, such forms being termed 

 accole or attached parasites. Eventually in all species the 

 parasite sinks into the substance of the cell. 



The subsequent development is identical with that pre- 

 viously described, the termination of which is the formation 

 of a schizont and the subsequent liberation of a number of 

 merozoites into the blood stream. This cycle may be repeated 

 any number of times until a large proportion of the red cells 

 is infected. 



The asexual method of multiplication in the blood of the 

 vertebrate host is characteristic of all species of Plasmodium. 

 By this means the infection is carried from one cell to another 

 within the vertebrate host, and very rapidly millions of the 

 blood corpuscles become infected. The destruction of the 

 blood cells thus entailed rapidly produces anaemia in the affected 

 patient, but much more harm is done by the waste products of 

 the parasites. These consist of the pigment granules and 

 various other products of metabolism which are left behind in 

 the residual protoplasm when schizogony occurs. As they 

 can only escape into the blood stream when the red cell 

 bursts, these various toxic waste products are liberated together 

 with the merozoites, and as most of the infected corpuscles 

 rupture about the same time, the effect of the accumulated 



