A STUDY of the utilization of lactose by the chick is of practical importance since milk and milk products are often fed to poultry, and of theoretical interest since this compound presumably plays a natural role only in the nutrition of mammals. The utilization of lactose must be considered not only in terms of rupturing the linkage which joins the galactose and glucose moieties, but also in terms of the utilization of the products derived therefrom. As glucose is a normal metabolite, the peculiar aspects of the problem may be related to lactose and galactose. Many animals have a limited ability to tolerate these sugars in the diet. One of the important factors which limits lactose utilization seems to be its effect on gastrointestinal motility (Fischer and Sutton, 1949). Apparently there are species differences and other factors which influence the level at which lactose produces diarrhea, but the symptom itself …