154 G. K- STEWAKT 



must have been a factor in maintaining the dilatation. Certain cardiac 

 irregularities have been observed to be modified in a striking manner when 

 the adrenal blood was shut off or allowed to enter the circulation (Fig. 

 22) (g). This indicates that the ordinary epinephrin output was in these 

 cases exerting an action upon the heart. There is a suggestion that the slow- 

 ing of the heart rate when, after previous section of the vagi, the acceler- 

 antes are cut, may be more constant and more marked when the output of 

 epinephrin from the suprarenals has been interfered with before section of 

 the heart nerves than when it is being discharged at the ordinary rate. 

 When the experiment is done in the reverse order, the extrinsic nerves of the 

 heart Being first severed, removal of the suprarenals is very commonly fol- 

 lowed by a slowing of the pulse, in which the loss of the ordinary epinephrin 

 output may be a factor (Cannon(e) 1919; Stewart and Rogoff() 1920). 

 It is quite true that the artificial injection of such quantities of epinephrin 

 as are ordinarily liberated from the suprarenals can produce only insignifi- 

 cant effects upon the circulation compared with the effects produced through 

 the cardio-regulative and the vasomotor nerves. And there is no reason 

 to believe that even when stimulated to the highest pitch, as by excitation of 

 the splanchnics or by strychnin, the direct action of epinephrin in raising 

 the blood-pressure can never be more than quite subordinate, in comparison 

 with the action of the nervous system. It does not follow that its action 

 is negligible, whether it be regarded as a factor of safety whose full weight, 

 small as it may be, when thrown into the scale in adverse circumstances in 

 which the nervous mechanism is crippled, may turn the balance, or as a 

 sensitizing influence which under normal conditions intensifies the nervous 

 action. The question might be asked whether epinephrin is not a survival, 

 now without much significance in the higher animals, from a stage of 

 development in which hormones carried in the circulation performed some 

 of the functions of the nervous system, which became more and more 

 predominant, as a much more rapid vehicle of communication, as develop- 

 ment proceeded. It may be that functionally epinephrin is more import- 

 ant in some lower vertebrates than in mammals. For example, Redfield's 

 (c) observations on a lizard, the horned toad, indicate that in the changes 

 in the color of the skin epinephrin may play a part in producing constric- 

 tion of the melanophore pigment. 



It may be taken as certain that whatever functions epinephrin may 

 perform they are not of such a nature that the abrupt suppression of the 

 epinephrin output of the suprarenals causes any gross and obvious change. 

 All the best evidence is to the effect that the blood-pressure remains prac- 

 tically unaltered for a time w r hen the suprarenal veins are carefully 

 clipped. There is not necessarily any fall of pressure when the glands 

 are carefully tied off or excised under anesthesia, or at any rate the 

 pressure curve does not show greater variations than in animals under 

 similar conditions in which the epinephrin discharge is proceeding. (For 



