282 Trans. Acad. Sci. of St. Louis. 



We see from these observations how difficult it is even 

 when great care is taken in using uniform methods to get 

 results that are strictly comparable. Certain bacteria are so 

 delicate in structure and so susceptible to conditions of en- 

 vironment that the composition and treatment of media is a 

 most important consideration. The constituents used in the 

 preparation of media which may vary greatly in quality from 

 time to time, the reaction of the medium, and even prolonged 

 and repeated sterilization are influences which contribute to 

 variations in the results and often lead to distinct cultural 

 characteristics. 



In the examination of water from different sources, it 

 is important to know which medium reaction is best adapted 

 or will give the highest efficiencv in bacterial numbers. It is 

 known that certain bacteria grow best on media of special re- 

 action, and in order to establish which reaction of media was 

 best suited for our work, special tests and comparisons were 

 made, and a few of the results are collected in Table VII. 

 In Table VIII will be found a summary of the results 

 on media made under uniform conditions, each of the five 

 lots of medium having a special reaction. 



