120 MEDULLA 



only slightly affected or dilated by epinephrine but Wiggers 680 

 claims that they are constricted. Similarly divergent results 

 have been obtained on isolated strips of cerebral arteries. 



It is difficult to ascertain the effect of epinephrine on the 

 coronary circulation of the intact heart, since the acceleration 

 of the pulse rate, the increased strength of ventricular contrac- 

 tion, and the increased blood pressure would all tend mechani- 

 cally to increase the blood flow through these vessels. Ac- 

 cording to Barbour and Prince 32 the coronaries of man and 

 the monkey are contracted by epinephrine while those of other 

 animals are dilated. 



The results of numerous studies on the effect of epinephrine 

 on various groups of vessels, have, as in the cases cited, in- 

 variably given the most diverse and conflicting results. These 

 discrepancies, as obtained in studies on the pulmonary vessels, 

 have been reviewed by Daly, 149 who has pointed out the many 

 factors which may lead to conflicting results: (1) the epineph- 

 rine preparation used; (2) variations in dosage; (3) the per- 

 fusion pressure and temperature; (4) the composition of the 

 perfusion fluid; (5) the tone of the blood vessels; (6) the animal 

 species experimented upon; (7) seasonal variations; (8) the 

 interpretation of the observations. The same factors undoubt- 

 edly have disturbed the experiments on other arteries. 



It must also be remembered that the results obtained on 

 dismembered anesthetized animals or on isolated tissues are 

 not indicative of the changes occuring in the normal animal 

 in which numerous reflexes allow compensatory adjustments, 

 which are absent in the anesthetized or operated animal, to 

 occur. The marked increase in the cardiac output following 

 epinephrine injections would speak for extensive dilatation of 

 the splanchnic and pulmonary vessels in the intact organism. 243 



The action of epinephrine is not limited to the arteries. 

 Many capillaries are constricted as may be noted by direct 

 observation. On the other hand, Dale and Richards 243 de- 

 scribed a capillary dilatation. The action of epinephrine on 



