PART III. 



THE STUDY OF BACTERIA 



CHAPTER XVI. 

 CULTURE MEDJA. 



The study of bacteria may be taken up for the disci- 

 plinary and pedagogic value of the study of a science; with 

 the purely scientific idea of extending the limits of knowl- 

 edge; or for the purpose of learning their beneficial or 

 injurious actions with the object of taking advantage of 

 the former and combating or preventing the latter. 



Since bacteria are classed as plants, their successful study 

 implies their cultivation on a suitable soil. A growth of 

 bacteria is called a "culture" and the "soil" or material 

 on which they are grown is called a "culture medium." 

 Insofar as the culture medium is made up in the laboratory 

 it is an "artificial culture medium" as distinguished from a 

 natural medium. A culture consisting of one kind of bac- 

 teria only is spoken of as a "pure culture," and accurate 

 knowledge of bacteria depends on obtaining them in "pure 

 culture." After getting a "pure culture" the special charac- 

 teristics of the organism must be ascertained in order to dis- 

 tinguish it from others. The discussion of the morphology 

 of bacteria in Chapters II, III and IV shows that the 

 morphological structures are too few to separate individual 

 kinds. They serve at best to enable groups of similarly 

 appearing forms to be arranged. Hence any further differ- 

 entiation must be based on a study of the physiology of the 



