60 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
Staphylococcus pyogenes albus and aureus are similar in 
so many respects that all are regarded by some bac- 
teriologists as different varieties of the same species. 
The optimum temperature for the udder cocci is 35 to 
37° C. (95 to 98.6° F.), but they grow well at much 
lower temperatures, development continuing down to 
freezing. The peptonizing action is exerted at these 
low temperatures. 
Many of the peptonizers are spore-forming bacteria. 
The most common representatives of this division are 
the hay bacillus (Bacillus subtilis) and the potato bacillus 
(Bacillus mesentericus vulgatus). They belong to a 
large group of organisms which are very numerous in 
cultivated soil and are consequently found on all products 
of the soil, especially hay, straw, roots, etc. They are 
large rod-shaped bacteria with rounded ends. The spores 
form in the middle or end of the organism without chang- 
ing its shape. On agar plates these bacteria form dry, 
thin, superficial skin-like colonies, with irregular borders. 
The colonies have a tendency to extend over the surface 
of the media and are consequently called “ spreaders.” 
These organisms are very numerous in the dust of hay 
and other dry fodder, also in straw, and they may get 
into the milk in large numbers if the fodder or litter is 
brought into the stable and distributed a short time before 
milking, or if dust from hay or other dry fodder is per- 
mitted to sift down into the stable through cracks in the 
ceiling. When a cow lies upon bedding or upon loose 
soil, these bacteria enter the folds and creases of the 
skin and become attached to the hair, and when the cow 
is milked those upon the udder, flanks and surrounding 
parts are dislodged and may fall into the milk pail. 
These organisms are especially numerous on the hair 
