THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 775 



ferent parts of the circulation are not equally sensitive to epinephrine ; 

 those of the splanchnic area are most sensitive, whereas those of the 

 heart the coronary vessels do not respond at all in most animals (see 

 page 268). The pulmonary and cerebral vessels have a variable reactivity 

 to epinephrine. 



The effect on the vessels persists after complete destruction, not only 

 of the central nervous system, but also of the vasomotor nerves; epi- 

 nephrine still acts, for example, on vessels the nerve fibers of which 

 have been allowed to degenerate by cutting them several days before the 

 epinephrine is applied. This would seem to indicate that the epinephrine 

 acts directly on the muscular tissue in the walls of the blood vessels, 

 but this does not appear to be the case, for it has been found that epi- 

 nephrine is incapable of acting on tissues which are devoid of sympathetic 

 nerve fibers, and is also inactive on those tissues in the embryo which have 

 not yet received any nerve supply. In brief, then, although epinephrine 

 acts only on blood vessels that are supplied by the sympathetic nervous 

 system, it is not on the nerve fibers that the epinephrine unfolds its 

 action. We shall see immediately that this conclusion is in conformity 

 with the results of observations made on structures other than the blood 

 vessels. 



Other muscular structures excited by epinephrine are as follows: 

 (1) the dilator muscle of the pupils, especially after the nerve supply has 

 been destroyed by extirpation of the superior cervical ganglion; (2) the 

 sphincters of the pylorus and of the ileocecal valve; (3) the muscle fibers 

 of the spleen, the vagina, the uterus, the vas deferens, and the retractor 

 penis. Regarding the action on the uterus, however, it should be noted 

 that a different response may be obtained according to whether the 

 uterus is pregnant or not. The plain muscles of the orbit and globe of 

 the eye are sometimes excited by suprarenal extract, causing the eyes to 

 protrude, the palpebral fissure to become large and the third eyelid to 

 be retracted, changes which are very like those which develop as a 

 result of fright. 



Inhibitory effects of epinephrine on muscle are exhibited by the follow- 

 ing: (1) the muscle of the intestine; (2) the stomach; (3) the esophagus; 

 (4) the gall and urinary bladders. 



The effect of epinephrine in inhibiting the rhythmic contractions of 

 isolated portion of the intestine in oxygenated Ringer's solution is a 

 rery striking phenomenon, and one which, as we shall see, may be very 

 successfully employed for detecting small quantities of epinephrine. 



The effects of epinephrine on glandular structures are the same as those 

 rhich would be produced by stimulation of the sympathetic nerve supply 

 of the gland. Thus, the secretions of the lachrymal gland, the salivary 



