204 BACTERIA, YEASTS, AND MOLDS 



body, and while able to grow in certain places are unable 

 to grow elsewhere. In these cases the disease produced 

 may be local, although secondary general symptoms may 

 appear, as is true of diphtheria. Between these two 

 extremes are many intermediate types. 



Whenever bacteria obtain a foothold in the body they 

 multiply more or less rapidly, and have the same general 

 power of forming decomposition products and secretions 

 as they have when growing in lifeless food. These new 

 substances arising in the body are as varied in nature as 

 are those produced by the common saprophytes. Among 

 them are almost sure to be some that are distinctly poi- 

 sonous, which we call toxins. These toxins may be either 

 decomposition products or bacterial secretions ; but how- 

 ever they are produced they are liable to be absorbed 

 by the blood, and the body may thus be directly poi- 

 soned by them. If the bacteria are in the blood itself, 

 this poisoning is easy to understand ; but localized dis- 

 eases are similarly explained. Diphtheria, for example, is 

 produced by bacteria growing on the inside surface in the 

 throat. The bacteria themselves do not enter the body, 

 but their excretions are absorbed rapidly enough. Grow- 

 ing in the throat, the bacteria develop very powerful 

 toxins, and these are absorbed from the throat into the 

 blood, producing a general poisoning of the whole body. 

 Sometimes the germs grow in the intestine (Asiatic chol- 

 era), and their poisonous secretions are absorbed with the 

 digested food. Something similar is true of practically all 

 disease germs. All produce poisonous materials which are 

 absorbed by the body, and these cause the direct injury 

 characteristic of the various diseases. 



