In the course of investigations on the production, distribution, and rate of disappearance in the body of immune substances, we were occupied in 1908 and previous years with a series of experiments on agglutinins, and we arrived at conclusions pointing to their close relationship to the blood and blood-forming organs (1, 2). In association with these inquiries, one of us (G. D.), together with W. Ray, published a communication on the relationship between the blood volume and the distribution of agglutinins within the circulation (3). It was there shown that the concentration of this substance (agglutinin) in the blood after inoculation into an animal was proportional to the body surface of the animal concerned, and was thus approximately proportional to the two-thirds power of the weight. Hence was deduced the conclusion that the blood volume of the animals examined was proportional to their body surface.