I Q2 CLINICAL BACTERIOLOGY AND KLEMATOLOGY 



The malarial parasite exhibits alternation of generations, there 

 being an asexual stage in the human being, and a sexual stage in 

 the mosquito. The latter terminates by the production of a number 

 of fine filamentous spore-like bodies (sporozo'ites), which enter the 

 red corpuscles, and develop into the amoeboid form (schizont, or 

 trophozoite amcebula) described above. This enlarges, sporulation 

 (schizogony) takes place, with the resulting formation of a crop of 

 spores (merozoites or euhaemospores). The red corpuscles rupture 

 and the merozoites are set free, and at this period the rigor takes 

 place. The merozoites enter more red corpuscles, go through the 

 same cycle, a rigor occurring each time the red corpuscles rupture and 

 discharge their crop of spores. This is the asexual cycle. 



There are three species of malaria parasite, each differing in the 

 length of time the spores take in maturing within the red corpuscles, 

 and, in consequence, the length of time between the rigors. Thus in 

 the tertian fever the cycle lasts forty-eight hours, rigors occurring on 

 the third day ; in the quartan, seventy-two hours, rigors occurring on 

 the fourth day ; in a third form, the malignant, or aestivo-autumnal, the 

 period is probably forty-eight hours, but the type of fever is irregular. 

 If mosquitoes bearing the tertian parasite bite a patient on two suc- 

 cessive days, he will develop quotidian fever, each crop of parasites 

 maturing on successive days; the same thing happens if he is inocu- 

 lated with quartan parasites on three following days. 



Another form of cell the sexual cell, or gametocyte is also formed 

 in man, but remains unaltered unless it enters the alimentary canal 

 of the mosquito. In the quartan and tertian types these sexual cells 

 are like mature amcebulse, whilst in the aestivo-autumnal form they 

 are the " crescents " already described. 



The sexual cycle takes place in the mosquito. The sexual cells, or 

 gametocytes, are sucked (with the blood containing them) into the 

 stomach of the mosquito, and there the differentiation into male and 

 female cells soon become manifest. The male cells protrude several 

 long flagella-like structures, which become detached, and then have 

 the power of independent movement. They contain chromatin, and 

 correspond to spermatozoa : they are known as microgametes. The 

 female cells become ready for impregnation by the extrusion of some 

 of their chromatin (corresponding to a polar body). Impregnation 

 is effected by the entry of the microgamete into the female cell, or 

 macrogamete, and the fusion of their chromatin, and the resulting 

 fertilized cell is called a zygote or ookinete (O, Fig. 32), 



This cell now leaves the cavity of the stomach and becomes encysted 

 between the muscle fibres, enlarges, and projects into the body cavity. 

 It now divides into a number of blastophores or sporoblasts, and these 

 again into a vast number of minute rod-shaped bodies known as 

 exotospores or sporozoi'tes (T, Fig. 32). 



The large cell now ruptures, and the sporozi'tes enter the body 

 cavity of the mosquito, and thence make their way to the veneno- 

 salivary gland, ready to be injected into a human being the next time 



