The subject of this paper is one that has interested pediatrists both in this country and in Germany for many years, but was brought forth anew for discussion a few years ago. It is hardly necessary to review the history of investigations in this field. The articles have been many, and almost all have included a summary of the numerous investigations which have considered the problem of casein digestion. It is well known that although Biedert regarded protein indigestion as the main obstacle to successful artificial feeding of infants, this conception has been completely disavowed by his fellow countrymen. The question was not allowed, however, to slumber long, but was aroused again by Talbot,1 who described large, hard masses in the stool, which he termed casein curds, believing them to be composed mainly of the casein of the milk. Without enumerating the various writers who immediately took sides on