632 MALARIAL FEVER 



protoplasm. They represent the male cells proper, that is, they 

 are sperm-cells or spermatgzoa ; they are also known as micro- 

 gametes. They become detached from the sphere and move 

 away in the surrounding fluid. In the female cell, which has 

 also assumed the rounded form, maturation takes place by the 

 giving off of part of the nuclear chromatin, this process corre- 

 sponding to the formation of a polar body. Impregnation occurs 

 by the entrance of a microgamete, the chromatin of the two cells 

 afterwards becoming fused. Impregnation was first observed 

 by McCallum in the case of halteridium, and he found that the 

 female cell afterwards acquired the power of independent move- 

 ment or became a "travelling vermicule." He also observed 

 the impregnation of the malignant parasite. The fertilised 

 female cell is now generally spoken of as a zygote or ookinete. 



It has been established that the phenomena just described 

 occur within the stomach of the mosquito, and that the fertilised 

 cell or zygote penetrates the stomach wall and settles between 

 the muscle fibres; on the second day after the mosquito has 

 ingested the infected blood, small rounded cells about 6 to 8 JJL 

 in diameter, and containing clumps of pigment, may be found in 

 this position. (It was, in fact, the character of the pigment 

 which led Ross to believe that he had before him a stage in the 

 development of the malarial parasite.) A distinct membrane 

 called a sporocyst forms around the zygote, and on subsequent 

 days a great increase in size takes place, the cysts coming to 

 project from the surface of the stomach into the body cavity. 

 The zygote divides into a number of cells called blastophores or 

 sporoblasts, and these again divide and form a large number of 

 filiform cells which have a radiate arrangement ; these were 

 called by Ross " germinal rods," but are now usually known as 

 sporozoites or exotospores (in contradistinction to the enhsemospores 

 of the human cycle). The full development (sporogony) within 

 the sporocyst occupies, in the case of proteosoma, about seven 

 days, in the case of the malarial parasites a little longer. 

 When fully developed the cyst measures about 60 /A in dia- 

 meter, and appears packed with sporozoites. It then bursts, and 

 the latter are set free in the body cavity. A large number settle 

 within the large veneno-salivary gland of the insect, and are thus 

 in a position to be injected along with its secretion into the 

 human subject. The sporozoites enter red corpuscles and become 

 trophozoites, as above described. Daniels found that, in the case 

 of the malignant parasite, an interval of twelve days at least 

 intervened between the time of feeding the mosquito and the. 

 appearance of the sporozoites in the glancl. 



