CREAM 337 



Later the lactic forms vanish also, and only fungi 

 remain. 



Ex. 153. Make a careful study of (i) the numbers and 

 (2) the kinds of bacteria in 

 (a) Freshly separated cream. 



(&} Well-ripened cream, thirty-six to forty-eight hours old. 

 (c) Cream left in a covered vessel away from dust for ten 



days. 



Dilute and plate out on litmus lactose gelatine and agar media 

 as described in Exs. 125, 126. 



What percentage produces acid or liquefies gelatine ? 

 Examine and prepare permanent stained slides of the various 

 colonies found. 



Grow pure cultures of the different kinds of organisms on agar 

 slants, and 



(i) Test the action of each upon : 

 0) Milk. 



(b) Nitrate bouillon. 



(c) Bouillon containing the various carbohydrates men- 



tioned in Ex. 147 (i). 



(ii) Test their power of producing indole (Ex. 63). 

 (iii) See if any give the Voges and Proskauer reaction (Ex. 65). 

 Classify and, as far as possible, name the organisms found, 

 comparing them with authentic examples. 



The ripening process is one of the greatest importance 

 from the dairyman's point of view : when it goes wrong 

 the butter frequently turns out to be objectionable in 

 flavour and aroma, and of poor keeping quality. En- 

 deavour should, therefore, be made to control it, and 

 although want of knowledge of many of its chemical and 

 bacteriological details makes exact direction impossible, 

 much can be done in a general way to guide it. 



Temperatures between 18.5 and 21 C. (65 to 70 F.) 



Y 



