Methods of Studying Bacteria. 27 



by the inoculation of pure cultures into experimental 

 animals, like rabbits, guinea pigs and white mice. 



The methods of the bacteriologist in his laboratory 

 are in their effect not dissimilar to those which the 

 farmer employs in securing his crop of pure-bred grain. 

 The laboratory farmer kills the weed seeds in his culture 

 field by the application of heat. His field, which is em- 

 braced in his culture dish, has been fertilized and pre- 

 pared by the addition of certain favorable ingredients. 

 When he has garnered his crop, he maintains its purity 

 by keeping his selected seed, the pure culture, free from 

 all contamination. The dairyman, even though he may 

 not expect to carry on the detailed operations of the 

 laboratory, will understand the reason for the directions 

 which he is often required to follow much better if he 

 knows how the .simple operations of the laboratory are 

 carried out. For a fuller knowledge of these matters, 

 the reader is referred to the special texts on bacteri- 

 ology. 



