192 E. G. HOSKINS 



sure. Whether the result is due to a true stimulation of the medulla by 

 the drug itself is doubtful, however. The pressor effect is quite plausibly 

 to be ascribed to the partial anemia produced in the center. That the 

 irritability of this center is augmented by interference with its local cir- 

 culation is easily demonstrated by such methods as ligation of the carotid 

 arteries. To what extent the pressor reaction to epinephrin may be de- 

 pendent upon stimulation of the sympathetic ganglia seems not to have 

 been satisfactorily determined beyond the fact that it is slight. Hkrtman 

 lias found that vasodilator effects, at any rate, may be obtained by apply- 

 ing epinephrin directly to sympathetic ganglia, 



Locus of Stimulation by Epinephrin 



As brought out in the preceding chapter, the action of epinephrin is 

 confined exclusively to tissues innervated by the sympathetic nervous 

 system proper (the thoracico-lumbar autonomic fibers of Langley). The 

 precise site of the stimulation has been much discussed. The essential 

 features of the pertinent evidence may be summarized. Of primary in- 

 terest is the fact that section and subsequent degeneration of the sym- 

 pathetic fibers do not abolish the epinephrin reaction, hence the central 

 nervous system and the ganglia play at most a minor role. On such 

 evidence as this Langley postulated that the effect of the drug is on the 

 smooth muscle directly. Later, Brodie and Dixon studied the matter 

 in more detail. It was discovered that apocodein, an alkaloid obtain- 

 able by dehydration of codein, has the property when given in large doses 

 of blocking sympathetic fibers. Thus it causes vasodilatation Tvith re- 

 sultant hypotension. Following the administration of apocodein, epine- 

 phrin fails to give a reaction. The application of barium chlorid or other 

 direct cell stimulant, however, shows that the smooth muscle itself is 

 still irritable. From these data it follows that the point of stimulation lies 

 between the sympathetic nerve terminals proper and the muscle cells. 

 The hypothetical element thus intervening in the myoneural junction has 

 been called by Langley the deceptive substance." It would seem to 

 correspond in function to the percussion cap of a loaded cartridge. Re- 

 garding the morphological nature of this myoneural junction, very little 

 is known. 



As to how epinephrin produces its effects, little beyond speculation 

 can be offered. It acts with astonishing promptness when applied to 

 such a sensitive tissue as a segment of rabbit intestine. When adminis- 

 tered intravenously, the latency of the reaction is not appreciably greater 

 than the time required for transportation of the drug to the reacting* 

 tissue. Whether the epinephrin enters into chemical combination with 

 the reacting tissue in the sense of becoming incorporated in the myo- 



