1. Extracts of the rabbit's kidney injected into the rabbit cause a slight, increase in blood pressure which is barely more than that due to the mechanical effect of the injection.
2. Extracts of the dog's kidney injected into the dog cause a decided fall in pressure; an equal fall may be caused by the dog's urine. A series of control experiments indicates that the fall caused by the kidney extract may be due to the urinary salts which it contains.
3. Extracts of cat's kidney cause a rise in pressure. As the cat's urine causes a fall, this rise in pressure indicates the possibility of a kidney extract containing a pressor substance which cannot be influenced by the depressor substance of the urine.
4. Rabbit's kidney, which in the rabbit produces a slight rise, when injected into the dog causes a drop comparable to that caused by the dog's kidney itself. Similarly, the dog's kidney, which injected into the dog causes a drop, produces in the rabbit a rise analogous to that produced by rabbit's kidney. It is evident therefore that these pressor and depressor substances of the kidneys in question do not have a constant effect on all animals as do the extracts of the adrenal gland.
5. Extracts of kidneys which are the seat of various forms of nephritis cause the same effect as extracts of normal kidneys.
6. The serum of dogs with considerable reduction of kidney substance causes a slight fall in pressure; the serum of dogs with spontaneous nephritis gives divergent results, as does also the serum of rabbits with various forms of acute nephritis. The serum of dogs with chromate nephritis causes a slight rise, while that of dogs with uranium nephritis produces a sharp and decided fall in pressure. Although there is no uniformity in these results, their general character, and especially the experience with uranium and chromate sera of the dog, suggests that pressure-disturbing substances are present in the serum as the result of the kidney lesion. The very slight evidence of the constant presence of a pressor substance, however, offers little support to the theory that such a substance is furnished by the diseased kidney or is due to disturbances of metabolism caused by disease of the kidney.