Lactic acid milks of one sort or another have been household remedies for centuries, and have been used critically by physicians for over a generation. Nevertheless, the exact reasons for their beneficial influence are unknown, and objections to their use are raised on theoretical grounds. Although infant feeding has progressed most when guided by observations of results in babies, rather than by attempts at chemical imitations of some preconceived ideal food, it was felt that more information concerning the chemical effects of lactic acid milk on the body is desirable.
The literature on the rôle of lactic acid in physiology is too large and manifold to present here, but it does seem desirable to keep in mind certain facts that are well recognized by physiologists. There are three types of lactic acid: (1) d-lactic acid which occurs as a normal metabolite of the body, and which is especially concerned with