FERMENTED 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, b.) These bacteria have been described as 
distinct species or varieties under many names. Among them may 
be mentioned Bacterium guntheri, Bacillus acidi lactici, and Strepto- 
coccus lacticus. In spite of th§ 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 ferment 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. 
8959°— Bull. 319—16 2 
