128 THE STORY OF GERM LIFE. 



mentation occurring in the vegetation that 

 brought about the chemical changes in it which 

 resulted in its transformation into coal. The vege- 

 tation of the carboniferous age was dependent 

 upon the nitrogen fixed by the bacteria, and to 

 these organisms also do we owe the fact that this 

 vegetation was stored for us in the rocks. 



CHAPTER V. 



PARASITIC BACTERIA AND THEIR RELATION TO 

 DISEASE. 



PERHAPS the most universally known fact in 

 regard to bacteria is that they are the cause of 

 disease. It is this fact that has made them ob- 

 jects of such wide interest. This is the side of 

 the subject that first attracted attention, has been 

 most studied, and in regard to which there has 

 been the greatest accumulation of evidence. So 

 persistently has the relation of bacteria to disease 

 been discussed and emphasized that the majority 

 of readers are hardly able to disassociate the two. 

 To most people the very word bacteria is almost 

 equivalent to disease, and the thought of swallow- 

 ing microbes in drinking water or milk is decid- 

 edly repugnant and alarming. In the public mind 

 it is only necessary to demonstrate that an article 

 holds bacteria to throw it under condemnation. 



We have already seen that bacteria are to be 

 regarded as agents for good, and that from their 

 fundamental relation to plant life they must be 

 looked upon as our friends rather than as our 

 enemies. It is true that there is another side to 



