FEKMENTED MILKS. 9 



not be below and may be a few degrees above blood heat. If in this 

 time the milk has not curdled with a sharp, acid taste and without 

 gas bubbles and whey there can be no reason for using these tablets 

 except the possibility that they contain the active element of the cul- 

 ture which retards the growth of other bacteria. The evidence on 

 this point is so inconclusive that it need not be considered in this con- 

 nection. 



All reliable manufacturers now place the date of manufacture on 

 each package and state the time within which the tablets should be 

 used. 



BUTTERMILK. 



Buttermilk, properly speaking, is the by-product resulting when 

 milk or cream is churned for butter. It is the milk remaining after 

 the fat which collects in granules is removed. If cream is churned 

 when sweet the buttermilk does not differ from ordinary skimmed 

 milk, but if it is churned when sour — the usual practice — the acidity 

 is sufficient to coagulate the casein in the cream. In the churning 

 process this curd is broken up into very fine particles. These curd 

 particles settle very slowly, and if the buttermilk is agitated occa- 

 sionally it will retain its milky appearance. When the buttermilk 

 is allowed to stand undisturbed for several hours the curd particles 

 sink to the bottom, leaving an opalescent whey at the top. At the 

 present time a large part of the so-called " buttermilk " sold in cities 

 is not buttermilk, properly speaking, since it is not made by churn- 

 ing cream, but is simply soured skimmed milk which has been 

 churned or stirred in order to break up the curd. The same product 

 is sold also under the name of " ripened milk." 



The souring of milk or cream is brought about by the activity of 

 certain bacteria which form lactic acid by decomposing the milk 

 sugar (lactose). The ability to form acid from lactose and other 

 sugars is possessed by many kinds of bacteria, but is so characteristic 

 of a certain group that they are commonly spoken of as the lactic- 

 acid bacteria. (See Fig. 1, 6.) These bacteria have been described as 

 distinct species or varieties under many names. Among them may 

 be mentioned Bacterium yuntheri, Bacillus acidi lactici, and Strepto- 

 coccus lacticus. In spite of the confusion in nomenclature it is 

 evident that the term "lactic-acid bacteria" includes a fairly well- 

 defined group of closely related varieties possessing in common several 

 definite characters. Variations from the type in minor characters 

 produce an almost infinite number of varieties. These variations may 

 be in the ability to fermeni different sugars, in the tendency to grow 

 in chains, in the kind of flavor formed in milk, in the intensity of acid 

 formation, and in the ability to produce pathological conditions in 



animals. 



8860°- Bull. 819 -16 2 



