RELATION SUPRARENAL GLANDS TO CIRCULATION 233 



had ceased dilating from the effect of the artificial heat, the quantity of 

 epinephrin previously administered now caused a distinct dilation. 



Hoskins, Rowley and Rosser studied the effects of hemorrhage upon 

 the response to epinephrin. By the injection of nicotin it was found that 

 the irritability of the vasomotor mechanism is increased by hemorrhage 

 of a degree to leave the blood-pressure at the normal level. Under these 

 conditions the reaction to epinephrin remained unchanged. With animals 

 subjected to a greater degree of hemorrhage, however, both Bardier and 

 Rous and Wilson found that the reaction was materially decreased. This 

 probably indicates merely that the vasomotor mechanism was under a 

 mechanical handicap incident to the loss of fluid. If the hemorrhage were 

 so profound as to result in marked and prolonged asphyxia of the reacting 

 tissues, it is to be supposed that the reaction would ultimately be decreased 

 as the reaction of any tissue to any type of stimulation is depressed under 

 the same condition. 



Snyder and Andrus observed reversal of the reaction to epinephrin 

 in the isolated heart of a terrapin when the hydrogen ion concentration 

 of the solution with which it was being perfused was changed. Thus 

 they found that epinephrin augmented the tonus evoked by a Ringer's 

 solution of pH. 7.8, but caused a diminution of tonus when the pH. was 

 7.0. Snyder and Campbell found likewise that a reversal of the con- 

 strictor effect of , epinephrin, when perfused through the circulation of the 

 frog, could be brought about by changes in hydrogen ion concentration. 

 Decreasing the acidity increased the vasoconstrictor effect and vice versa. 



Gruber was unable to obtain vasodilatation in limb vessels the nerves 

 to which had just been severed, although this was easily evoked in the 

 normal limb. He concluded that lack of vasodilator action was due to 

 loss of tonicity in the vascular musculature. The vasodilator reaction 

 again appeared as the vessels regained tonicity, as they do in time after 

 denervation. 



Collip(c) (1921) has reported observations which perhaps explain the 

 failure of earlier observers to note the depressor effects of epinephrin. 

 It was noted that reversal of the depressor action could be effected in dogs 

 merely by increasing the depth of the anesthetic. The depressor effect 

 again returned when light anesthesia was resumed. The reversal could 

 be brought about very quickly, particularly with ether anesthesia, though 

 also somewhat more slowly with chloroform. By alternating between light 

 and deep anesthesia reversal could be obtained time after time. That the 

 reversal is not due to changes in the concentration of the anesthetic per se 

 is indicated by the fact that the reversal appeared with striking prompt- 

 ness. The phenomenon could not be associated with changes of blood- 

 pressure, reversals being easily elicited while this was maintained at a 

 constant level. Collip also extended Snyder' s observations on the relation 

 of hydrogen ion concentration to this yasornotor reversal, It was found in 



