THE MALARIAL PARASITE 179 



like contractions of its body, or by wriggling forward by spiral 

 undulations, or by a gliding movement. Under the same 

 conditions it has been seen to penetrate a red blood corpuscle 

 by one of its pointed ends and to gradually work its way in, 

 the whole process lasting about forty minutes. When it has 

 entered the corpuscle the sporozoite assumes a rounded shape 

 and becomes a trophozoite. It soon exhibits active amoeboid 

 movements and grows in size at the expense of the substance 

 of the corpuscle. A characteristic feature of its earlier stages 

 is the appearance in the neighbourhood of the nucleus of a 

 large vacuole, which, as it looks transparent in comparison 

 with the surrounding cytoplasm, gives the parasite the shape 

 of a ring (fig. 38, ///). It is probable that this vacuole is in 

 some way connected with the nutritive processes. 



The young trophozoite is unpigmented, but as it grows, 

 granules of a dark brown pigment termed melanin are de- 

 posited in its cytoplasm. The amoeboid movements gradually 

 become slower and finally cease, and the trophozoite when it 

 has attained its full size nearly fills the blood corpuscle. Thus 

 far its growth has been purely vegetative, but it now proceeds 

 to multiply by division, a process which in these forms is 

 known as schizogony, and the individual ready to enter upon 

 division is called a schizont. The nucleus divides, apparently 

 by a primitive form of mitosis (fig. 38, Vl\ and the two 

 nuclei so formed divide again and again till some dozen or 

 sixteen nuclei are present. The melanin granules become 

 aggregated in the centre of the cell-body, and the cytoplasm 

 then segments into as many corpuscles as there are nuclei, a 

 small amount of residual protoplasm containing the melanin 

 granules being left in the centre. In this manner a number 

 of reproductive bodies named merozoites are formed. They 

 escape from the remains of the blood corpuscle into the 

 plasma, and at once attack and make their way into fresh 

 corpuscles, boring their way into them in the same manner 

 as did the sporozoite. On obtaining an entrance they become 

 trophozoites, go through the same phases of growth and 

 division as those just described, and in due time give rise 

 to a new crop of merozoites, which in their turn infect fresh 

 blood corpuscles. 



At least three kinds of malarial fever are recognised by the 

 medical profession, the tertian and quartan agues, and the 



