As is well known, the glomeruli of the frog’s kidney are supplied with blood only by the renal arteries, whereas the renal tubules have a double supply. On the one hand, they receive blood by way of the renal portal veins; on the other hand, the efferent vessels from the glomeruli open into the capillary network round the tubules. The whole of the tubule receives blood from each of these two sources, so that the capillary network around the tubules can be fully injected either from the renal arteries or from the renal portal veins. Taking advantage of this fact it has been shown by Beddard and one of us (F. A. B.) that after complete occlusion of the glomeruli the tubules, when adequately supplied with oxygen, maintain their normal histological appearance, and may secrete urine. In the present experiments an attempt has been made to determine the function of the glomerulus and to ascertain whether the tubules possess the capacity to absorb water and solids.