UNICELLULAR ORGANISMS 71 



into twelve to sixteen small spores, as is shown; / to g. The 

 blood corpuscle now breaks to pieces and the spores are liberated 

 into the liquid blood h. Each may then make its way into a 

 new corpuscle and repeat again the history as already described. 



Although this animal in its general structure and shape is 

 much like the Amceba, its habits are totally different. While 

 growing in the red blood corpuscles of the human body, it pro- 

 duces the disease which is known as malaria, chills and fever, 

 or fever and ague. The period when the chills occur corresponds 

 to the time when the blood corpuscles have broken up and the 

 spores are liberated into the blood. The organism may continue 

 to repeat the above history time after time in the blood of the 

 same person, the spores after being liberated entering into new 

 corpuscles, and again repeating their life cycle almost indefinitely 

 and prolonging the disease. There are three different species of 

 the malarial organisms, distinguished by the different length of 

 time required for their life cycles. The most common form takes 

 48 hours, a second species takes 72 hours, and a third is irregular. 



By the method of reproduction above described, this organism 

 may multiply inside the blood of one person but is unable to 

 pass to a second individual. Malaria is therefore not communi- 

 cable as long as this process alone is repeated. But after a time, 

 for some unknown reason, the organisms in the corpuscles assume 

 two different forms shown in Figure 25 at g to i. One of them 

 grows into a large rounded mass, while the other develops sev- 

 eral long motile, thread-like bodies, which become detached. No 

 further change occurs unless the patient is now bitten by a cer- 

 tain kind of mosquito (Anopheles). If the blood of a patient 

 is swallowed by this mosquito, the malarial organisms undergo 

 a new series of changes. % The thread-like bodies become de- 

 tached from the mass that produces them, and one of them unites 

 with one of the larger rounded masses, j and k. This union is 

 regarded as a sex union (see Chapter XII), the larger rounded 

 mass being the female cell (or egg) and the thread-like body the 

 male cell (or sperm) in the sexual union. After the thread-like 



