x INTRODUCTION 



of urban infantile mortality, and of the control of 

 contagious diseases are all bound up with the intelli- 

 gent application of bacteriological methods. 



In the almost untilled field of industrial bacteri- 

 ology there is need for a fuller appreciation of the 

 value of bacteriological methods and principles. 

 Many great industries are based wholly upon the 

 proper selection and adaptation of micro-organisms, 

 and a timely and discriminating utilization of their 

 products. Loose and empirical methods have been 

 in force in the past, but these must eventually give 

 way to a more precise and truly bacteriological 

 technique. 



Agricultural bacteriology is just now much in the 

 public eye, and it would be gratuitous to prophesy 

 the results that may reasonably be anticipated in 

 this direction. Here again crude, rule-of-thumb, 

 " practical" ways of doing things are being sup- 

 planted by the scientific, the reasoning, and the 

 precise. 



To the student, whether in medical, hygienic, or 

 industrial bacteriology, proper technical methods 

 of work must always have a peculiar value, since 

 without their aid advance is impossible, and stumb- 

 ling and disastrous missteps are certain. A com- 

 prehensive outline of modern bacteriological methods, 

 therefore, is a necessary adjunct to obtaining a true 

 and full understanding of the underlying principles 

 and tendencies of the science. The technique of 



