GROWTH AND PRODUCTS OF BACTERIA 23 



tion of the toxins of the causative germ, and in many 

 instances most of the symptoms of the disease may be 

 so reproduced. 



Protozoa are minute unicellular animal organisms 

 closely allied to bacteria, but differing from them in 

 their mode of reproduction. They pass through a com- 

 plicated life-cycle which has been followed completely 

 only in the malarial protozoa. There occurs first an 

 asexual cycle or reproduction which takes place in man, 

 wherein each parasite breaks up into six to twenty 

 spores or daughter-cells, which rapidly develop into 

 full-grown parasites. The periods of chills, fever, and 

 sweats of malaria correspond to these periods of repro- 

 duction of the parasite. Then there occurs a sexual 

 cycle which takes place in an intermediate host, the 

 mosquito. Male and female elements are represented 

 in this cycle and a peculiar spore formed, which, when 

 injected into man, develops into the complete organism 

 and proceeds to pass through the asexual cycle again. 



