IX] LIFE-CYCLE OF MALARIAL PARASITE 12/ 



containing a single nucleus, but soon a "vacuole" appears in 

 the parasite, causing it to assume a ring form (Fig. 40, i). 



As^the parasite grows it feeds on the substance of the red 

 coipuscle, and gradually destroys the whole cell, but during 

 this process certain waste products are formed, one of which 

 is deposited within the cytoplasm of the growing trophozoite 

 in the form of pigment granules. These granules are composed 

 of a brown or black substance allied to melanin, to which the 

 name " haemozoin " is sometimes applied. This substance is 

 chiefly the result of the decomposition of the haemoglobin, and 

 has very pronounced physiological properties, being mainly 

 responsible for the febrile attacks that occur in patients suffer- 

 ing from malaria. 



The trophozoite grows until it reaches a certain size — about 

 three-quarters the diameter of the red cell — when it becomes 

 rounded off and withdraws all pseudopodia. The full grown 

 trophozoite is then known as the schizont, and consists of a 

 rounded mass of cytoplasm containing numerous pigment 

 granules and a nucleus situated to one side of the centre. This 

 nucleus now begins to divide, according to the species of Plas- 

 modium, into 6 to 20 spialler nuclei (Fig. 40, 5), which become 

 arranged around the periphery of the parasite. Each of the 

 nuclei then becomes surrounded by a mass of cytoplasm which 

 separates off from the remainder, and thus a number of small 

 parasites are formed. These are known as the merozoites and 

 are usually ovoid bodies, about 2/Lt by i/u, each containing a 

 single nucleus. In the above-described process a certain 

 amount of cytoplasm, containing all the pigment granules, 

 is left unsegmented at the centre of the cell. After segmen- 

 tation is complete the wall of the red cell bursts and the mero- 

 zoites, together with the residual protoplasm and pigment 

 granules, escape into the blood stream. 



Many of the merozoites are now ingested by the leucocytes, 

 but a certain number escape and at once proceed to attack other 

 red cells. Unlike the sporozoite, the merozoite does not 

 directly bore its way into the red cell, but usually becomes 

 attached to the surface of the cell. 



Very soon after the young parasite has attached itself, its 



