The terms employed in a definition of milk vary with the view point of the scientist and the phase of the subject emphasized. For the present purpose the following, gleaned from various sources, will answer every need: Milk is a normal animal secretion forming a perfect emulsion and containing, besides fat globules in suspension, albumin, sugar and salts in solution, caseinogen in partial solution and certain ferments. Except for the one which produces lactic-acid fermentation, comparatively little is known of the ferments of milk.
The importance of these ferments is very great. Two classes seem apparent in recently drawn milk: Those expending themselves directly on the milk, and those relating more especially to the intrinsic food value of the milk. The latter speak of the kinship between milk and normal coursing blood, of which it is the most direct of all products.
These ferments are of delicate organization and, like
McALISTER A. THE GREATEST MENACE TO WHOLE MILK IN CITIES' SUPPLY.. JAMA. 1907;XLIX(16):1342-1344. doi:10.1001/jama.1907.25320160020001d