As previously stated, von den Velden has contended that shortening of coagulation time by adrenin is due to exudation of tissue juices resulting from vasoconstriction. The amount of adrenin which produces markedly faster clotting in the cat, is approximately 0.001 milligram per kilo. As Lyman and I[105] showed, however, this amount when injected slowly, as in the present experiments, results in brief vasodilation rather than vasoconstriction. Von den Velden’s explanation can therefore not be applied to these experiments. He has claimed, furthermore, that adrenin added to blood _in vitro_ makes it clot more rapidly, but, as already noted, he gives no account of the conditions of his experiments and no figures. It is impossible, therefore, to criticise them. His claim, however, is contrary to Wiggers’s[106] earlier observations that blood with added adrenin coagulated no more quickly than blood with an equal amount of added physiological salt solution. Also contrary to this claim are the following two experiments: (1) Ligatures were tied around the aorta and inferior vena cava immediately above the diaphragm, and thus the circulation was confined almost completely to the anterior part of the animal. Indeed, since the posterior part ceases to function in the absence of blood supply, the preparation may be called an “anterior animal.” When such a preparation was made and 0.5 cubic centimeter of adrenin, 1:100,000 (half the usual dose, because, roughly, half an animal), was injected slowly into one of the jugulars, coagulation was not shortened. Whereas for a half-hour before the injection the clotting time averaged 4.6 minutes, for an hour thereafter the average was 5.3 minutes--a prolongation which may have been due, not to any influence of adrenin, but to failure of the blood to circulate through the intestines and liver.[107] In another experiment after the gastro-intestinal canal and liver had been removed from the animal, the average time for coagulation during twenty-five minutes before injecting adrenin (0.23 cubic centimeter, 1:100,000, in an animal weighing originally 2.3 kilos) was 5.5 minutes, and during forty minutes after the injection it was 6.8 minutes, with no case shorter than 6 minutes. In the absence of circulation through the abdominal viscera, therefore, adrenin fails to shorten the clotting time. (2) The cannulas were filled with adrenin, 1:1,000, and emptied just before being introduced into the artery. The small amount of adrenin left on the walls was thus automatically mixed with the drawn blood. Alternate observations with these cannulas wet by adrenin and with the usual dry cannulas showed no noteworthy distinction. Feb. 19. 2.21--6 minutes, with usual cannula .30--6.5 “ “ “ “ .36--6.5 “ “ adrenin “ .49--6 “ “ “ “ .56--7 “ “ usual “ 3.04--6 “ “ adrenin “