“…Intra-arterial injections of 45-75 jug histamine (ten experiments) or 5-10 mg acetylcholine (ten experiments) during the 3rd min following the insertion of the fingers into the cold, that is, when the cold vasoconstriction was well established, did not cause a premature vasodilatation (Fig. 2a, b), although smaller doses of histamine always, and of acetylcholine usually, cause a large increase in hand blood flow at 32°C (Duff, Greenfield, Shepherd & Thompson, 1953). The complete or almost complete arrest of the circulation during the first few minutes of immersion in the cold water (Greenfield & Shepherd, 1950) must, however, restrict the amount of drug reaching the finger.…”