CHAPTER IV. 



THE METHODS OF ISOLATION AND PURE 

 CULTURE OF BACTERIA. 



Method of Isolation. In nature various species of 

 bacteria are met with mixed together, much as we find 

 different kinds of plants distributed in a natural pasture 

 or wood. But just as it is possible to separate from a 

 meadow any single flowering plant and grow it so as to get 

 a large collection of plants all of the same species, so it 

 is possible to isolate and cultivate a single species of 

 bacterium. A collection of bacteria consisting of indi- 

 viduals all alike, i.e. belonging to the same species, and 

 free from admixture with any other kinds is termed a 

 pure culture. It is only by the study of bacteria in pure 

 cultures that their form, mode of growth, physiological 

 activity, and other features can be determined. 



The general principles underlying the separation of 



bacteria and their pure culture may now be described, 



but in order to obtain a thorough acquaintance with the 



work the student must carefully work through the 



s practical exercises appended. 



The bacteria to be isolated will perhaps most 

 frequently be distributed in solutions of some sort such 

 as milk or water : where they are present in a solid 

 material, say cheese, butter, or soil, a small portion of 

 the material must be broken up and shaken with pure 

 sterilized water. 



