On examining fresh specimens of white rats' blood containing numerous trypanosomes of a strain (T. brucei group), for which I am indebted to Dr J. W. Scott Macfie and with which I was experimenting at the Medical Research Institute at Yaba, Nigeria, I was struck by the energetic way in which the parasites attacked the red blood corpuscles. They sometimes adhered to the corpuscles for a long time, moving them about in different ways, and sometimes appeared to pierce their membrane, now in one place, now in another, penetrating more or less deeply into their substance. A careful search of a number of stained films revealed in some the presence of very interesting appearances which seem to establish the important fact that these trypanosomes are capable of ingesting and digesting erythrocytes. The accompanying figures, which are all from one and the same specimen taken six days after intraperitoneal infection, show that the parasite encircles the erythrocyte, which gradually becomes enclosed in its protoplasm, probably in a sort of vacuole which develops between the two nuclei. The erythrocyte becomes more or less disintegrated and gradually reduced in size; its characteristic staining remains for a long time recognizable, but the final result is a vacuole with homogeneous, almost unstained contents, between trophonucleus and kinetonucleus.