PROTOZOA 7 



with the above mentioned toxins, that causes the chill. This process 

 of sporulation, which continues at very regular intervals, sets free into 

 the blood three types of spores which, for convenience may be termed 

 male, female and neutral. If, now, a culex mosquito sucks the blood 

 containing these spores, they are all digested along with the blood, in 

 the mosquito's stomach; if, however, it be an anopheles, instead of some 

 other genus, that sucks the blood, different results follow. In the 

 anopheles' stomach the neutral forms are digested, along with the 

 blood, but the male and female cells conjugate and form a cyst or 

 nodule in the wall of the stomach. This cyst breaks down into many 

 perhaps ten thousand tiny sporozoites, and as there may be hundreds 

 of cysts in one mosquito the number of sporozoites is enormous. After 

 ten days or more these sporozoites collect in the mosquito's salivary 

 glands, where they may live for two or three weeks, during which time, 

 if the mosquito bite a human being she will inject into the wound some 

 of the sporozoites, and the life cycle is begun again in another victim. 

 Several persons may be infected by the same mosquito. 



It has been found that, under certain conditions, the sporozoon 

 may remain dormant in the spleen or bone marrow for months or 

 years, where it can resist the action of quinine, the universally used 

 specific for malaria; under favorable conditions it may resume its 

 activities and the person will suffer a relapse. 



Not only has this life-history of the parasite been very carefully 

 worked out, but numerous practical tests have been made that prove 

 very conclusively that malaria is not " caught" from mists, drinking 

 water, etc. For example, wherever malaria is found, excepting sporadic 

 cases that may be introduced from other regions, the anopheles is found. 

 There are sections where this mosquito exists without malaria, simply 

 because nobody has introduced the disease into that region. The 

 reason for the prevalence of malaria in swampy regions is, of course, 

 that it is in such places that mosquitoes abound. 



The experiments of Grassi, the Italian, will serve as an example of 

 many similar experiments. "In 1900 he received permission from the 

 government to experiment on the employees of a piece of railroad that 

 was being built through a malarial region. This was divided for the 

 purposes of the experiment into three sections, a protected zone in the 

 middle and an unprotected zone at each end. Those working in the 

 protected zone had their houses completely screened and no one was 



