MILK FERMENTATIONS 85 



cultures. Instead of the ordinary culture tube, tubas open at 

 both ends are made from glass tubing. These are stoppered 

 at the lower end with rubber stoppers, but otherwise they are 

 treated as usual. The inoculation of the medium is as usual. 

 Care should be taken to heat the medium for some time in 

 boiling water to expel the dissolved oxygen, to mix very 

 thoroughly with the melted medium the substance to be 

 examined, and to solidify the inoculated medium quickly. 



After incubation, those tubes which do not show too 

 numerous colonies, and from which it is desired to make 

 subcultures, have the agar removed by withdrawing the 

 rubber stopper and pushing the agar core into a sterile 

 Petri dish by means of a sterile glass rod. The agar can 

 then be divided with a sterile knife, so as to render any 

 particular colony accessible. 



Exercise. Each student will heat to 80 C. for fifteen minutes a 

 sample of milk inoculated with a small amount of soil. Incubate at 

 37 C. If the milk undergoes an acid fermentation, isolate the causal 

 organism by the method described. Make a detailed cultural, morpho- 

 logical, and biochemical study pf the organism. 



