ESSAYS OK BACTERIOLOGY. 115 



considerable migration of bacteria within the body is 

 brought aboxit only by transport through the various 

 body fluids. 



Bacteria multiply by the process of fission or split- 

 tiag, one cell, by this simple process, giving rise to 

 two, four or more daughter cells, which have or soon 

 assume all of the properties of the parent. In addi- 

 tion to this process of splitting, they reproduce them- 

 selves by spore or seed formation, one cell giving rise 

 to one spore, the latter proceeding at once to develop 

 into a ihature bacterium, or lying dormant until the 

 conditions' for its full development are present. As a 

 rule, these spores are much more tenacious of life than 

 the mature bacteria, are much more resistant to hos- 

 tile influences, and therefore more independent of 

 their environment. For these reasons spores will 

 often resist drying, and degrees of cold and heat, even 

 to freezing, or boiling for a time, such as would rap- 

 idly destroy the fully developed organisms. In this 

 spore stage, bacteria, like other seeds, may frequently 

 retain their life, while not growing nor mutiplying, 

 for long periods. Such facts often explain the in- 

 sidious persistence of infectious material even under 

 apparently adverse conditions. The seeds of various 

 grains lie dry and' cold in the bin during the winter, 

 ready to sprout with the advent of spring. And so 

 with the seeds of disease. . 



Various theories have been proposed to explain the 

 disease-producing acti'vity of micro-organisms. Most 



