CHAPTER V. 



THE BACTERIA AS MAN'S INVISIBLE FOES. 



WE have seen that the bacteria in general 

 are not only curious and interesting 

 as objects of study, but in the work which they 

 are ceaselessly and silently doing they are ab- 

 solutely indispensable to the continuance of 

 the higher forms of life upon the earth. But 

 unfortunately there is another darker side to 

 the picture. Among the myriads of useful as 

 well as harmless bacteria, we have lately 

 learned that there are a few forms which find 

 the most favorable conditions for their life and 

 growth in the bodies of men and some of the 

 higher animals. 



They do not grow well in nature as other 

 bacteria do, nor do they thrive on ordinary 

 decomposing organic matter. They look very 

 much like the more common harmless bacteria, 

 some being little balls, some rods, and some 



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