SECRETION OF MILK 



703 



The average composition of cow's milk, taken from a very large number 

 of analyses, is: 87.2 per cent water, 12.8 per. cent solids, 3.0 per cent casein, 

 0.5 per cent albumin, 3.7 per cent fat, 4.9 per cent sugar and 0.7 per cent 

 mineral constituents. 



Woman's milk contains: 87-89 per cent water, 10.8-12.4 per cent solids, 

 1-2 per cent proteid, 3-4 per cent fat, 5-8 per cent sugar and 0.2-0.4 per 

 cent mineral matter. 



In general woman's milk is poorer in proteid and mineral constituents and 

 richer in sugar and lecithin than cow's milk. The absolute quantity of milk 

 secreted during the lactation period increases up to the twenty-eighth week, 

 and then falls off. The proteid content, however, shows an almost constant 

 decrease, as the following figures from Soldner will show. Part of the data 

 are from different individuals. 



The fat content likewise decreases somewhat in the course of the lactation 

 period; but the percentage of sugar increases, at first pretty rapidly, then 

 more and more slowly. 



According to Bunge the mineral constituents of woman's milk have the 

 following distribution per 1,000 parts: K 2 0.703, N"a 2 0.257, CaO 0.343, 

 MgO 0.065, Fe,0 3 0.006, P 2 5 0.469, Cl 0.445. 



The quantity of milk secreted daily by both breasts of a nursing mother 

 may be estimated at about 1,300 g., but this quantity is subject to great 

 variations. 



B. SECRETION OF MILK 



The milk is secreted by the mammary glands. Each gland consists of 

 15-20 lobes grouped about as many ducts which open in the nipple. They 



