96 SOME MINUTE ANIMAL PARASITES 



travel in the body fluids until they reach the salivary 

 glands of their host, where they collect in great 

 numbers. The mosquito has now become fully in- 

 fective, and its saliva contains enormous numbers of 

 parasites. The mosquito cycle takes about ten days. 



Desiring yet more food, the Anopheline flies away 

 in search of a victim. This time it encounters a 

 white-skinned individual a child or a man, perhaps 

 insufficiently protected, while sleeping, by a 

 mosquito-net. The insect stabs some exposed spot, 

 and as it pierces the skin, the saliva, heavily charged 

 with the sporozoites, passes into the wound and 

 reaches the blood-stream. The mosquito having 

 satisfied its needs, flies away to propagate its species. 

 The victim remains quiet, but after some days is 

 destined to know of the action of the insect by 

 undergoing an attack of " fever," otherwise malaria. 



Once within the human blood the sporozoites 

 attack the red corpuscles, and according to the way 

 in which they behave, so is the progress of the 

 disease in the human victim. The malarial parasites 

 are certainly remarkable for their numerous forms and 

 appearances (Fig. 23). Having once invaded a red 

 blood-corpuscle, the sporozoite becomes rounded, and 

 grows at the expense of the corpuscle. In its early 

 life it is distinguished by having a large space in its 

 body, probably caused by a vacuole, which gives it a 

 characteristic "signet-ring" appearance (Fig. 23, A). 

 As it grows, the ringlike form becomes less evident 

 and the parasite appears more compact, but is 

 amoeboid (Fig. 23, B). Gradually it produces the 

 dark pigment (Fig. 23, B-F, p.) which is so 



