PART V. 

 PARASITIC BACTERIA. 



CHAPTER XIV. 



RESISTANCE AGAINST BACTERIA. 

 ANTHRAX. 



PARASITIC BACTERIA IN GENERAL. 



IN the previous parts of this work we have seen that 

 some bacteria are capable of living upon purely inorganic 

 food and are therefore wholly independent of other living 

 organisms. These bacteria doubtless play an important part 

 in the soil transformations and probably in rock disintegra- 

 tion. A second class of bacteria feed upon the lifeless bodies 

 of animals and plants. These, which we call saprophytes, 

 are the great agents for disintegration of organic substances, 

 and are a vital part of agricultural processes. We have now 

 to notice a third class of bacteria, also of great interest to 

 agriculture, which are capable of living in and feeding upon 

 living animals and plants. This enables them to exist within 

 the bodies of animals and plants and makes them parasitic. 

 Their existence involves an entirely new set of phenomena for 

 consideration. We have learned in the previous chapters that 

 bacteria are, in general, to be regarded as the allies rather than 

 the enemies of the agriculturist. This is true for the first 

 two classes of bacteria, but for the group of parasitic bacteria 

 the reverse is the case, for these are almost universally the foes 

 of agriculture. 



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