ISOLATION AND CULTIVATION 99 



A mixed or impure colony. This is a growth in which 

 two or more individual organisms of different species multi- 

 ply together on a solid medium giving a visible growth sug- 

 gesting in many instances that produced by a single indi- 

 vidual. Mixed colonies frequently occur and give rise to 

 much confusion in the further study of the organism. When, 

 however, the two or more organisms develop a growth dif- 

 fering in color or any other obvious character they are 

 readily detected; but with two organisms which have a 

 similar appearing growth on the medium, it is difficult and 

 sometimes impossible to know that the colony is impure 

 without further study. 



A culture of bacteria. A culture is the growth or mul- 

 tiplication of organisms on some nutrient medium. It usu- 

 ally refers to- it in a tube or other retainer for media. 



A pure culture. This is the growth or multiplication of 

 a single species of bacteria upon a medium that was sterile 

 before inoculation. 



A mixed or impure culture. This is the growth or multi- 

 plication of two or more species together in a single medium. 

 Thus the bacillus of typhoid and the colon bacillus grow- 

 ing together in a tube of bouillon would be an impure bouil- 

 lon culture. 



Procuring pure cultures. A pure culture of an organism 

 is obtained by inoculating media from pure colonies or from 

 a substance containing but one species of bacteria. Thus 

 glanders nodules in the lungs or other organs are not likely 

 to have bacteria within them other than Bact. mallei. 



Making bouillon cultures. In making this culture, care- 

 fully remove the plug from the tube of bouillon by first 

 twisting it around to detach any adhesions and then pull it 

 straight out. Pass the open end of the tilted tube quickly 

 through the gas flame. The plug, which has in the meantime 

 been carefully held, is partially replaced and the tube re- 

 turned to its stand. Treat the tube containing the culture 

 in the same manner. Then place the two tubes side by side 

 between the thumb and forefinger of the left hand, palm 



