. University of Toronto studies. Physiological series. no. 1-98. 1900-28 . on between the denervated and normal limbsis not due, as Gunning (8) suggests, to extreme dilatation of the dener-vated limb resulting from the absence of vasoconstrictor impulses. Adepressor substance obtained from ox pituitaries was injected into theanimal that produced figures 1 and 2. The dilatation of the denervatedlimb was as great as that in the normal limb, showing that the limit hadnot been reached. 358 FRANK A. HARTMAN AND LOIS McP. FRASER In one dog (17 kgm.) a plethysmograph was placed sohind limb just above
. University of Toronto studies. Physiological series. no. 1-98. 1900-28 . on between the denervated and normal limbsis not due, as Gunning (8) suggests, to extreme dilatation of the dener-vated limb resulting from the absence of vasoconstrictor impulses. Adepressor substance obtained from ox pituitaries was injected into theanimal that produced figures 1 and 2. The dilatation of the denervatedlimb was as great as that in the normal limb, showing that the limit hadnot been reached. 358 FRANK A. HARTMAN AND LOIS McP. FRASER In one dog (17 kgm.) a plethysmograph was placed sohind limb just above the ankle. Adrenalin was injectedlation. As a result the limb was constricted as much asinstance and as little as cc. in another. Withoutplethysmograph both femoral and sciatic nerves to thewere then severed. The same amount of adrenalin ( injected as before with a resulting constriction of 1every instance. Moreover the duration of constriction as to include ainto the cc. in onedisturbing the enclosed limbcc, 1 : 10,000)cc. or more in in the dener-. Fig. 3. Same as figure 1 in response to cc. adrenalin, 1:10,000. (Reduced f.) vated limb was almost twice as long as that before cutting centralnervous connection (fig. 4). The greater and more prolonged constric-tion, after the nerves were cut, was no doubt due to absence of dilata-tion from central nervous influence. This explanation also probablyapplies to one of the cats which failed to give dilatation in the normallimb, for the constriction in the normal limb was always decidedly lessthan in the denervated limb. We attempted to demonstrate the necessity of central nervous con-nection for dilatation from adrenalin in another way. The dose which MECHANISM OF ADRENALIN VASODILATATION 359 gave the maximum fall in blood pressure was determined. A number ofinjections were made so that the average might be found. After cut-ting the nerves to the limbs the percentage fall in blood pressure from
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