OBSERVATIONS ON THE DEPRESSOR EXTRACTS OF HUMAN BLOOD AND ON THE VASCULAR ACTION OF EXTRACTS OF RABBIT AND DOG BLOOD.

1. Alcoholic extracts of the plasma of rabbits obtained from arterial or venous blood differ from those of human plasma in having a marked depressor action on the blood pressure of anesthetized cats. This action is unantagonized on atropinization. Extracts of the plasma of dogs, on the other hand, are almost without vascular effect. 2. Ultrafiltrates of the plasma of rabbits are actively vasodepressor, while those of human and dog plasma are without action. 3. Extracts of the plasma of rabbits reduce the renal volume greatly and they have a relatively weak dilator action on the arteries of the periphery. These effects resemble those of adenylic acid more than those of histamine. 4. It is possible that the pressor-depressor substances of the blood are species-specific. 5. Human plasma, ascitic and spinal fluid which have been allowed to stand, yield extracts that are depressor and in their pharmacological action resemble closely extracts prepared from red blood cells and acetic acid extracts of tissues. Their constrictor effect on the kidneys is marked. 6. Histamine, choline, and adenosine depress the level of the blood pressure more effectively than they constrict the volume of the kidneys, while the reverse is true when adenylic acid is employed.