274 FERMENTATIONS IN MILK 



introduced into milk, souring takes place rather slowly. In 

 a day or two at a temperature of 30 to 40 C., coagulation 

 occurs, and the curd which is precipitated contains a few 

 small gas bubbles, the serum which separates being clear. 

 The taste and odour developed are generally disagreeable. 

 Lactic acid is formed and often with it occurs a fair 

 amount of acetic acid as well as traces of formic and 

 succinic acids and alcohol. Many troubles of the dairy- 

 man in butter-making and cheese-making can be traced 

 to organisms belonging to this group. 



The following are the chief characters of typical Bact. acidi 

 accici, Hueppe. 



Size and Form. Rods i to i J /* long and f to i /x broad in pairs 

 and chains. 



Gelatine. Surface colonies round or lobed, white and moist 

 and slimy, very similar to those of B. coli. Deep colonies, small, 

 usually spindle-shaped. 



Agar. Irregular, greyish, shining ; deep colonies, small, round 

 or spindle-shaped. 



Potato. Abundant growth, greyish at first, then yellow or 

 brown, 



Bouillon. Turbid with abundant sediment. 



Milk. Acid produced and curd precipitated with a few small 

 bubbles in it. 



Sugar Bouillon. It ferments glucose and lactose with acid 

 and gas production, but not saccharose. 



Indole is produced by it in peptone solution (Ex. 63), but it does 

 not give the Voges and Proskauer reaction (Ex. 65). 



A form which appears to be almost as common as 

 the type already described and very closely allied to it, 

 is known as Bacterium lactis aerogenes, Esch. It was 

 first isolated from the milk-stools or faecal matter of 



