Malaria 87 



nearly all cases, but are sometimes two or three inches 

 in diameter or length. They consist of a single, 

 nucleated cell. They are found almost everywhere, 

 mostly in water, especially when it is stagnant, 

 but a certain number, comparatively few, however, 

 exist as parasites. In spite of their minuteness, 

 these latter little creatures are far more to be feared 

 than wolves or tigers, for they not only have caused 

 terrific epidemics among fish, birds, silkworms, do- 

 mestic and other animals, but have also slain their 

 tens of thousands among the human race. 



The life of the individual protozoan is but a few 

 hours, yet these organisms are commonly said to be 

 immortal, although some time ago I saw an account of 

 an ameba which disintegrated. Perhaps it was at- 

 tacked by bacteria, although this is merely a guess. 

 However, the protozoan, at the end of some hours, or 

 possibly one or two days, divides into two or more 

 distinct animals. It has not died, but as an individual 

 it has disappeared. This process of reproduction is 

 varied occasionally by conjugation of two of the 

 creatures which come together, exchange half their 

 nuclei, then separate, and go on dividing again. Con- 

 jugation, as has been proved by experiment, is neces- 

 sary to the rejuvenescence and immortal life of the 

 protozoan. Division cannot be continued indefi- 

 nitely without an occasional interchanging of nuclear 

 substance. 



The malaria protozoan belongs to the group of 

 spore producers, or sporozoa, and depends on a host 

 for the life cycle. Without a host the sporozoa will 

 die — this not being the case with bacteria, which, 



