874 PHYSIOLOGY OF DIGESTION AND SECRETION. 



of the skin or the intestine. In accordance with the generaHzation 

 that epinephrin acts only or mainly upon the endings of the sym- 

 pathetic autonomic fibers, this result is interpreted to mean that 

 the heart muscle and the skeletal muscle are supplied with vaso- 

 dilator fibers. Stimulation of the endings of these fibers by the 

 epinephrin causes therefore vascular inhibition or dilatation. On 

 the plain muscle in other organs epinephrin has a somewhat variable 

 effect, differing with conditions or with the animal selected. The 

 uterine musculature, for example, in the pregnant cat is made to 

 contract, but in the non-prgenant condition it shows relaxation. 

 The plain muscle of the bronchioles exhibits relaxation under the in- 

 fluence of the epinephrin, and since these muscles probably receive 

 their nerve-supply through the bulbar autonomics (vagus) their re- 

 action to epinephrin indicates that the above generalization in re- 

 gard to the sympathetic autonomics must not be understood to 

 mean that the epinephrin acts only on the musculature innervated 

 by the sjnnpathetics, but rather that the muscle so innervated 

 shows a special response to epinephrin action. Even skeletal mus- 

 cles are distinctly affected by epinephrin. Under the influence of 

 appropriate doses, the contractions are increased in size and the sub- 

 sequent relaxation seems to be more rapid and complete. In addi- 

 tion to its influence on the muscular or neuromuscular mechanisms 

 epinephrin has an effect upon the body metaboHsm, especially as 

 regards the carbohydrates. When injected it causes an output of 

 sugar in the urine, which may last for some days. Evidently the 

 epinephrin, in these overdoses, interferes in some way with the 

 sugar-regulating mechanism of the body. Along with the glyco- 

 suria there is hyperglycemia, that is, an increase in the sugar- 

 content of the blood, and the usual explanation for this action of 

 the epinephrin is that it stimulates the process of glycogenolysis, 

 the process by which the stored glycogen of the liver is converted to 

 sugar and given to the blood. This production of epinephrin 

 glycosuria has been observed not only under experimental condi- 

 tions, but also under what may be called normal conditions in which 

 there is evidence of an increased secretion or hypersecretion of the 

 gland. Cannon has described, for example, what he calls emotional 

 glycosuria, a condition in which in consequence of emotional 

 excitement there is an increased secretory activity of the adrenal 

 gland and an accompanying glycosuria. Results of this kind would 

 seem to indicate that the normal secretion of epinephrin may play 

 a part in the complex sugar-regulating mechanism of the body, 

 and there is evidence, which will be referred to briefly later, that 

 the other glands of internal secretion, or some of them at any rate, 

 are also concerned in the regulation of the sugar supply and sugar 

 consumption. When administered in large doses epinephrin has a 



