iv EXPERIMENTAL DAIRY BACTERIOLOGY 



view, and each would supplement the other. Sucli studies, 

 however, are better adapted to the advanced student than to 

 the beginner, and it is felt that it is preferable to present to 

 the elementary student the biologic aspect of the subject 

 more or less completely divorced from the practical factory 

 work. The technique of bacteriological methods should be 

 mastered by each student individually. He should learn how 

 to make his media, and how to care for the same. After this 

 necessary technical foundation has been laid, it is possible to 

 make certain experiments in groups, and thus economize in 

 time and material with no loss in pedagogic value. 



The methods presented are believed to be the best in use 

 at the present time. A committee of the American Public 

 Health Association now has under consideration the formula- 

 tion of standard methods for milk analysis, but these have not 

 as yet been published. The methods of media making are 

 those recommended by the Laboratory Section of the Ameri- 

 can Public Health Association, and, while more complicated 

 than those usually described in text-books, are surely more 

 desirable in establishing uniform methods. 



In bacteriology, as in other biological sciences, unknown 

 factors must be dealt with. Again, numerous conditions that 

 cannot be controlled influence the results. A long series of 

 observations may be certain to point in a definite direction, 

 while one or two observations, such as can be made in a course 

 of study, may give results wholly at variance with what is 

 expected. This fact does not, however, lessen the value of the 

 exercise in training the student in technique and in develop- 

 ing his power of observation. 



