Fermentations of Milk'. 99 



by the growth. Red milk may be due to bacteria, but 

 more frequently is caused by the actual presence of 

 blood in the milk, due to a wound in the udder, or the 

 effect of a severe case of inflammation of this gland. 

 Such a condition may be readily distinguished by al- 

 lowing the milk to stand for a short time, in which 

 case, if due to blood, the red corpuscles will soon settle to 

 the bottom of the container, while bacterial troubles pro- 

 ducing a red coloration are more evident on the surface. 



It is also claimed that certain bacteria may impart v a 

 soapy taste or turnip flavor to milk. 



Cycle of fermentations in milk. If a sample of milk 

 is allowed to stand, it will undergo a certain sequence of 

 fermentations that well illustrates the principle that one 

 type of organisms is dependent on some other type to 

 furnish suitable conditions for its development. This 

 cycle of changes that normally occurs in milk is as fol- 

 lows: (1) The bacteria that come from the interior of 

 the udder are the first to develop, but usually the change 

 they produce is not evident. 



(2) Of the types that gain admission, subsequent to 

 the milking, the acid-producing species are able to ad- 

 just themselves most perfectly to the conditions that ob- 

 tain in milk. Within a few hours they greatly predomi- 

 nate and soon the milk curdles under the production of 

 acid. Their growth, however, is soon stopped by the ac- 

 cumulation of their own by-products. 



(3) The semi-solid curdled milk, on account of its 

 acid reaction then becomes a favorable medium for the 

 growth of molds; a prevalent form, known as Oidium 

 lactis usually develops as a white velvety layer. The 

 molds in their growth form alkaline by-products, which 

 tend to neutralize the acid reaction, so that in the course' 



