There is probably no other single food that has been submitted to as many chemical analyses as has cow's milk. There are published records of literally thousands of such examinations of samples from a corresponding large number of the lactating animals. From such data it has become clear that market milk, though representing the normal secretion of a physiologically functioning gland, varies widely in its composition. The variations are probably distinctly greater than those of the bloods from which in ultimate analysis the milk is derived.
In view of these facts it should not be surprising that human milk, derived as it is from a species far less "standardized" in respect to both "breed" and "feed," has been found to vary in composition between wide limits.1 A recent writer2 reminds us that among the conditions demonstrably effective in altering the quantity and quality of the milk secreted are
HUMAN MILK STUDIES. JAMA. 1931;97(21):1540. doi:10.1001/jama.1931.02730210038012