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-peptonizers. 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-peptonizers 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 
