THE STORY OF THE BACTERIA. 53 



spirals. Like other bacteria, they grow at the 

 expense of the materials with which, under 

 favorable conditions, they come in contact, and 

 like them they produce new chemical com- 

 pounds as the result of their life processes. 

 When they get into the human body, the dif- 

 ferent forms grow in different ways, and pro- 

 duce different kinds of chemical compounds, 

 and this growth or the poisonous chemical 

 compounds which are produced cause disease. 



Bacteria which can grow in the body and 

 produce deleterious effects there are called 

 pathogenic or disease-producing bacteria. The 

 poisonous chemical compounds which they set 

 free as they grow, are called ptomaines. 



Now, before we try to comprehend how 

 disease can be produced by bacteria, we ought 

 to understand what disease is. 



We have seen in the first chapter that the 

 human body is made up of several communi 

 ties of cells, each community having acquired 

 the power of doing some special thing for the 

 good of the body as a whole, and that these 

 cell communities are all co-ordinated so as to 

 act in harmony. We have seen that these 



