THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 737 



substance which reacts with epinephrine. This substance may be pro- 

 duced either at the junction between the nerve and muscle the myo- 

 neural junction, or perhaps throughout the protoplasm itself. It is 

 called the receptor substance of Langley, and is believed to react not 

 only with epinephrine, but also with various drugs. The receptor sub- 

 stance seems to increase, if not in amount, at least in sensitivity after 

 the removal of the nerve control. 



Ergotoxin, which is an amine obtained from ergot and also from cer- 

 tain of the products of histidine, has an action on the receptor substance 

 which is inhibitory and therefore antagonistic to that of epinephrine. 



The antagonistic action of ergotoxin affects the excitatory but not 

 the inhibitory actions of epinephrine. By using this drug we are en- 

 abled to show that, although the main effect of epinephrine on tissue is 

 excitatory, a less marked inhibitory influence may be simultaneously 

 developed. The inhibitory effect may also sometimes be evoked by 

 doses of epinephrine very much smaller than those used to produce 

 excitatory effects. These facts are well illustrated in the case of the 

 muscle fiber of the blood vessels. With an ordinary dose of epinephrine 

 constriction occurs; after ergotoxin the same dose of epinephrine causes 

 dilatation. Or this latter result may also be obtained by administer- 

 ing to a normal animal quantities of epinephrine that are very much 

 smaller than the usual quantity. The coexistence of inhibitory and ex- 

 citatory influence is also well noted in the case of the uterus. In some 

 animals the effect of epinephrine on this organ is to augment its rhythmic 

 contractions, in others to inhibit them. In the former case, however, if 

 ergotoxin is first of all administered, epinephrine in its usual dosage will 

 invariably produce an inhibitory effect. The ergotoxin no doubt acts on 

 the receptor substance, and similar effects have also been produced with 

 apocodeine. 



Although it is especially on plain muscular fiber having a sympathetic 

 nerve supply that epinephrine unfolds its action, yet, according to Can- 

 non, it increases the contracting power of voluntary muscle and dimin- 

 ishes the tendency to fatigue.* 



"For further details of these effects the papers of Iloskins"-' and IIartniaii r ' 1 should be consulted. 



