BACTERIA OF MILK 59 



of this type of decomposition, the milk acquires a bitter 

 taste (peptones) and later the taste and odor are foul 

 and unpleasant. Some of the decomposition products 

 are capable of exerting an injurious effect upon persons 

 drinking the milk. Nausea and vomiting may occur, 

 even in adults, when the taste is only bitter and before it 

 has become decidedly foul. The reaction of the milk is 

 usually alkaline, but some of the peptonizers are acid- 

 formers and curdle milk by souring it. 



Included in this group are certain of the cocci which 

 appear to be constantly present in the lower parts of the 

 cow's udder and are consequently called udder cocci. 

 These organisms are to be found regularly in milk when 

 it comes from the udder, especially in the fore milk. 

 They are present in greater proportion in milk produced 

 under good conditions than in ordinary milk. There are 

 many varieties or species of these organisms which differ 

 principally in their fermentative properties and in the color 

 of their colonies. In milk hygiene, it is desirable to 

 divide them into peptonizers and non-pep tonizers. Part 

 of the peptonizers first curdle milk and then digest the 

 curd ; others bring about digestion without previous cur- 

 dling. Some of the organisms which curdle the milk do 

 so by means of a rennet-like ferment ; the others by means 

 of acid resulting from fermentation of the lactose (acid 

 peptonizers) . The non-pep tonizers are practically inert, 

 producing no apparent change in milk. On agar plates, 

 the udder cocci form small, irregularly round colonies 

 which are usually white. The colonies of Staphylococcus 

 pyogenes albus vary from white to cream color, while 

 those of Staphylococcus pyogenes aureus are orange- 

 yellow. The latter two organisms are peptonizers and 

 also form lactic acid. The ordinary udder cocci and 



