46 THE GERM THEORY OF DISEASE. 



adaptation, is the human body, and the spores of which can 

 pass from one person to another, either by contact or through 

 the air, and cause disease in others. 



MIASMATIC CONTAGION. 



A third class partakes of the nature of both, but differs 

 from both. It is supposed to be an organism which has one 

 period of development in the human body and another period 

 without the human body, and that these two stages are 

 required for its full development. Therefore, such diseases 

 are not contagious; they cannot pass from one to another 

 until they have found a suitable soil for the second stage of 

 development and completed their spores. When this has 

 been accomplished, they are again ready for the production of 

 the disease in man, and not before. 



In this way whole regions of country become infected, and 

 persons are struck down with the disease without having seen 

 one sick of it, or having been very near them. Cholera, Yellow 

 Fever, Typhoid Fever, and various other diseases belong to 

 this class. They are called miasmatic contagious diseases. 



This theory is not based upon any demonstration yet made, 

 either in the human subject or upon animals, but rests upon 

 the known life history of certain parasites of the vegetable 

 kingdom and circumstantial evidence. 



Among the most familiar and best proven of the vegetable 

 parasites which run through this kind of cycle, is the 

 common uredo or rust on wheat. This parasite requires two 

 separate growths to complete its spores. Indeed, it seems to 

 have a double set of spores. The spore formed on wheat 

 will not again grow upon wheat, but will grow on the leaves 

 of certain bushes, especially the barberry bush. And the 

 spores formed on these bushes will, in turn, grow on wheat, 

 thus completing its cycle of existence. 



