Cultivation and Identification of Bacteria 117 



is called the inoculum and the resultant growth, whether it be in 

 a liquid or in a solid medium, is termed a culture, or subculture. 

 If the transfer is made to a solid medium, the visible growth which 

 appears after a suitable incubation period is a colony. If but one 

 species of organism is involved in this cultivation technic, it is said 

 to be a PURE cultl^re. A single kind of organism may be isolated 



Fig. 23. Colonies developing on nutrient agar exposed for ten 

 minutes to the air in a classroom. {By permission frotn Introduction to 

 the Bacteria by C. E. Clifton. Copyright, 1950. McGraw-Hill Book 

 Company, Inc.) 



from mixtures of organisms by a purification process to be discussed 

 in this chapter. 



Attempts to study the metabolism of a single bacterial cell are 

 impractical, in fact, probably impossible. But by cultivating 

 masses of organisms, as long as they arise from a single cell or 

 from a group of like organisms, the results of a study can be relied 

 upon, and reproducible reactions are possible. It therefore be- 

 comes important to grow volumes of bacteria by employing the 

 prerequisites of a good microbiological medium discussed pre- 



