10 



Bacteria in Relation to Country Life 



Diseases like tuberculosis, diphtheria, typhoid, cholera, 

 pleuro-pneumonia and leprosy were proved to be due 

 to specific organisms isolated and studied in pure culture. 

 The rapid advance of bacteriology within the last 

 quarter of a century has carried investigations beyond 

 the isolation of pure cultures of various bacteria. Chem- 

 istry has become a strong ally of bacteriology, and has 



Fig. 1. Soil-bacteriological investigations at the New Jersey Experiment Station. 



enabled the latter to recognize the chemical transfor- 

 mations effected by the microorganisms. Medical 

 bacteriology saw a, wonderful development in the study 

 of toxins, the poisonous substances resulting from 

 bacterial activities, and anti-toxins, capable of neutral- 

 izing these poisons. This, in turn, has been the starting 

 point for far-reaching investigations concerning the 

 invasion of the animal system by bacteria, and the 

 protective machinery of the living body. 



We have learnecl much concerning the powers of 



