699 
erroneous. Even now its exact composition, beyond the relative pro- 
portions of its constituents, is imperfectly understood. 
According to the most recent analyses of Pfeiffer, Koenig, Leeds, 
Harrington, Adriance, and others the average composition of human 
milk is as follows : 
Composition of woman's milk. 
Percent- 
age. 
Common nor- 
mal varia- 
tions. 
Fat 
4.00 
7.00 
1. 50 
.20 
87. 30 
100. 00 
Per cent. 
3.00- 5.00 
6.00- 7.00 
1.00- 2.25 
.18- .25 
89.82- 85.50 
100.00 100.00 
Sugar 
Proteids 
Salts 
Water 
An average caloric value per kilogram, 710.5 calories; common normal variations of 
caloric value per kilogram, 550 calories to 844.25 calories. 
Former analyses have for the most part assigned to it a higher 
amount of proteid and a lesser amount of sugar than this. The 
composition of milk is pretty nearly constant throughout lactation, 
except during the first month and toward the close. At the com- 
mencement of lactation the proteids and salts are high, and near its 
end the proteids have a tendency to diminish (Adriance). 
Proteids . — Our knowledge of the proteids of woman’s milk is still 
incomplete. The most important proteid substances, however, are 
casein and lactalbumen. Some investigators mention a third, lacto- 
globulin. The casein is in chemical combination as calcium casein, 
and owing to its relative proportions to the other proteids is only 
slightly precipitated by dilute acids and not appreciably* coagulated 
by rennet. 
The lactalbumen is believed to be similar to serumglobulin. 
The proportions of lactalbumen to casein have not been definitely 
agreed upon, but it exists in far greater proportions relative to the 
casein than in cow’s milk. According to Koenig, the relative propor- 
tions are as 5 to 4. The total amount of proteids varies normally 
from 1 to 2 per cent and abnormally from 0.07 to 4.5 per cent. They 
are highest during the first few days of lactation ; after the first few 
weeks they vary but little until toward its end, when they experience 
a decided decrease. 
Fat . — Fat is present in woman’s milk in the form of minute glob- 
ules, and in perfect emulsion by virtue of the albuminous fluid in 
which they are suspended. It exists mainly in the form of the neu- 
tral fatSj olein, palmitin, and stearin, and but small quantities of 
