Many investigators, seeking after an explanation of the methods by which nutritive material is carried from the alimentary tract to the different tissues and organs of the body, have called attention to the possible importance of the white corpuscles in the assimilation of food-stuffs, citing the fact that in a well nourished carnivorous animal there is a marked production of new cells in the lymph spaces of the intestinal mucous membrane after the ingestion of food, the extent of said production being apparently dependent upon the amount of assimilable elements contained in the food. It has been further supposed that this increased production of lymph cells is followed by a corresponding increase in the passage of leucocytes into the blood, mainly on the ground that only a comparatively few of the cells could have any local action in aiding the nutrition of the intestinal walls. There has been, however, a lack of positive proof of these assumptions until Pohl,[2] in his studies on the absorption and assimilation of food-stuffs, took up the matter experimentally, and sought to obtain some positive data bearing on the question. This investigator made a careful study of the physiological variations in the content of leucocytes in dog’s blood, using young animals and feeding them only one meal a day. The leucocytes were counted after Thoma’s method, preliminary experiments showing that there was very little difference in the number of white cells contained in a given volume of arterial or venous blood. Thus, in the case of a fasting animal, blood taken from the jugular vein contained 16,378 white corpuscles per cubic millimeter, while blood from the carotid artery of the same side contained 15,449 white cells per cubic millimeter. Further, from a well-fed animal, whose blood was examined during digestion, similar results were obtained, _i. e._, 27,036 from the jugular vein, and 26,866 from the carotid, thus showing that blood from the capillaries of either veins or arteries would give essentially the same results. A single experiment, illustrative of the many reported by Pohl, may be given here, as showing the marked effect of food upon the number of white corpuscles in the circulating blood: Time. Number white corpuscles per cubic millimeter blood. 9 A. M. 8,689 9 A. M. 100 grams meat fed. 10 A. M. 16,685 11 A. M. 17,296 5 P. M. 7,256 Maximal increase, 99 per cent.