DISEASES CAUSED BY ONE-CELLED ANIMALS 127 



When a mosquito "bites," that is, pierces the skin with 

 its needle-like mouth-parts, so as to suck blood, it always 

 pours a little of the fluid from the salivary glands into the 

 woxmd. The reason for this is not certainly known, but the 

 fluid, perhaps, keeps the blood from coagulating and thus 

 from refusing to. flow. However, one of the results of this 

 habit is to inoculate the bitten person with the germs of 



9®o 



Fig. so. Diagrammatic figure of stages in the development of the malaria- 

 producing Haemamoeba {Plasmodium) in a red blood-corpuscle of 

 the huBian body. 



malaria, for some of the many quiet httle spindle-shaped 

 germs flow into the blood with the salivary fluid. 



As soon as they enter the blood they become active and 

 attach themselves to the red blood -corpuscles and burrow 

 into them. As they work their way into the corpiiscles 

 they change their shape gradually, getting shorter and 

 thicker, until by the time a germ is well lodged within a 

 blood-corpuscle it is nearly spherical. 



