PHARMACOLOGY AND TOXICOLOGY OF SUPRARENALS 253 



hours later than this. They found that 

 good epinephrin reactions could be ob- 

 tained in limbs denervated two and 

 three months before. They concluded 

 therefore that epinephrin must act 

 upon nerve endings which are consid- 

 ered to be connecting links between 

 nerve and muscle rather than merely 

 fine branches of nerve fibers purely 

 nervous in structure. In others words 

 this connecting link which they call 

 the neuromuscular junction (myo- 

 neural junction, Elliott) does not de- 

 generate following section of the 

 nerve. 



The two antagonistic sets of fibers 

 in the sympathetic connect with myo- 

 neural junctions which are sensitive to 

 epinephrin. Thus, in turn, the vaso- 

 constrictors and vasodilators to the 

 same part may be brought into action 

 by the use of epinephrin (see effect 

 of epinephrin on the circulation). The 

 response of the vasconstrictor myo- 

 neural junctions is easily demonstrated 

 in a perfused organ or in isolated ves- 

 sels. Vasodilator myoneural junctions 

 can be similarly demonstrated in a 

 perfused organ and also in a part to 

 which the nerves have been cut. How- 

 ever, in the last instance either the 

 part must be perfused or else a few 

 days must elapse after denervation in 

 order to bring out the dilator response 

 (Figs. 6 and 7). 



Gangliar Mechanism. It has been 

 shown by Hartman and Fraser that 

 the action of epinephrin is not limited 

 to the myoneural junction. By per- 

 fusing the limb or the intestinal loop 

 in which the nerves are intact but in 

 which all connection with the blood 

 stream is cut off, dilatation can be 

 obtained from the injection of epineph 



Fig. 6. Reversal of the epinephrin 

 response in a freshly denervated limb 

 by perfusion. Upper record circula- 

 tion to limbs intact, 1.0 c.c. epinephrin, 

 1:10,000 injected into the jugular vein. 

 Lower record limbs perfused, 2.0 c.c. 

 epinephrin, 1:10,000 injected into the 

 perfusion fluid. Dog 24 kgm. (Re- 

 duced one-half.) (After Hartman, 

 Kilborn and Fraser, Amer. Journ. Phy- 

 siol.) 



rin into the jugular vein. 



