705 
that of a laboratory incubator, which is one of the chief causes of 
the high degree of diarrheal mortality during the summer months 
of the infants to which it is fed. Instead of the phrase “ milk warm 
from the cow,” so common in popular literature, we must substitute 
the words “ milk cold from the cow ” and see to it that they become 
an actuality. 
COMPOSITION or cow’s MILK. 
The composition of cow’s milk from different breeds varies chiefly 
in the content of butter fat, the other ingredients being remarkably 
constant in their proportions. Holstein cattle produce milk with 
the lowest fat content (3 per cent) and Jersey cattle that with the 
highest (5 per cent). According to the analyses of Richmond, 
Fleischmann, United States Experiment Station, Adxiance, and 
others, good herd milk has the following average composition : 
Average herd milk of good quality. 
Fat 
Proteids 
Salts 
Sugar 
Water 
Per cent. 
4.00 
. 3.50 
.75 
. 4.50 
. 87. 25 
100. 00 
Caloric value per kilogram, 700 calories. 
Physical characteristics of cow’s milk. Its color is white, varying 
from a clear to a yellowish white. It is very opaque, the opacity 
being due to its large content of calcium in combination with its 
casein. Its specific gravity varies from 1.028 to 1.033, with an aver- 
age of 1.031. Its taste is pleasant and characteristic. The addition 
of acetic acid causes a flocculent precipitate, and on the addition of 
rennet it coagulates into a firm mass. 
Reaction . — When freshly drawn this is amphoteric or slightly 
alkaline ; on standing it soon becomes acid. 
Proteids . — The proteids of cow’s milk consist mostly of casein in 
combination with calcium. As in woman’s milk, lactalbumen is 
also present but in small quantity. According to Koenig, casein is 
present in the proportion of 7 to 1 as compared to lactalbumen. 
Fat . — The fat in cow’s milk is the element that is most subject to 
variation, as the content of the other food elements is remarkably 
constant. A milk poor in butter fat contains about 3 per cent, while 
a rich milk, such as milk from Jersey cows, contains 5 to 5.25 per 
cent of fat. It is highly important to know the percentage of fat 
present in milk actually being used for the feeding of infants, for 
reasons discussed later on. 
45276°— Bull. 56—12 45 
