34 EXPERIMENTAL DAIRY BACTERIOLOGY 



growth. From the tube culture after the incubation inocu- 

 lations can be made into various media. 



Liquid cultures. These are made in nutrient broth, 

 milk, etc. 



Stab cultures are made in solid gelatin and agar by in- 

 fecting the end of the needle with a bit of the growth from 

 the colony or previous culture, and thrusting the needle for 



INOCULATING TUBE CULTURES 



The cotton plugs should be held in such a manner that the lower part will not 

 come in contact with the hand, and so they can be easily replaced 



nearly its entire length into the medium and withdrawing. 

 The gelatin should not crack on insertion of the needle ; if 

 it does so, a fresh tube must be melted in warm water and 

 resolidified in cold water. The cracking is due to the drying 

 out of the upper layers of the gelatin in the tube. 



The culture of the organism must be kept pure. During 

 the various manipulations the cultures are constantly exposed 



