40 The Story of the Bacteria 



characteristics. We can plant them under 

 such conditions that their oxygen supply is 

 limited, and learn whether they do or do not 

 thrive; we can see whether they grow best at 

 high or low temperatures, whether they form 

 gas or not, and what degrees of heat or cold 

 will kill them. We can grow them in large 

 quantities, and study the chemical compounds 

 which result from their life processes. We can 

 apply to them various chemical substances 

 which are called germicides, or disinfectants, 

 and find out to which of these and in what 

 strength they most readily succumb. 



In this way a large number of different 

 species of bacteria have been studied, and 

 these have been arranged in groups which 

 have some characters in common. So that 

 already, although the study of the bacteria by 

 the new methods is of recent date, we have the 

 outline of analysis tables, something like those 

 made for the identification of the higher 

 plants in Gray's Botany, for instance, by 

 the use of which the student can identify 

 certain of the better known forms which he 

 may come across in his studies. 



