ADRENALS 66l 



the iris of the cat's eye after removal of the superior cervical ganglion. 

 When the pupil has been dilated by epinephrin, the dilatation passes off 

 sooner if the adrenal vein blood is prevented from entering the circula- 

 tion. This shows that the dilatation of the pupil must have been in 

 part sustained by the epinephrin continuously entering the blood from 

 the adrenal veins. 



The suggestion that enough epinephrin may be continuously liberated 

 to exert an influence upon the nutrition and metabolism of the sym- 

 pathetic system, or of the myoneural junction, which is necessary for 

 normal excitability, without ever rising to the threshold of actual 

 excitation, is a mere hypothesis, and a hypothesis which does not seem 

 easily reconciled with the result of Hoskins, that after ligation of the 

 adrenals the excitability of the vaso-motors remains absolutely un- 

 diminished. 



It has been supposed by some that although usually liberated in an 

 amount too small to cause demonstrable effects, epinephrin ca.n be dis- 

 charged at a greatly increased rate under certain conditions for 

 example, under emotional stress (the so-called emergency function of 

 epinephrin). There is no evidence, however, that such outbursts 

 of epinephrin ever occur, and experimentally it is by no means easy 

 to produce decided alterations in the rate of discharge. 



Whatever the function of epinephrin may be, it is not indispens- 

 able for life and health. For cats after removal of one adrenal and 

 section of the nerves which govern the epinephrin discharge from 

 the other, not only survive indefinitely, but show no apparent differ- 

 ences from normal animals, although, when the nerve section is com- 

 plete, no epinephrin can be detected by the most delicate tests in the 

 adrenal vein blood, and the possible concentration in the arterial 

 blood cannot at most amount to I : 100 thousand millions. 



Nervous Mechanism Controlling the Liberation of Epinephrin. 

 The spontaneous liberation of epinephrin from the adrenals is 

 entirely dependent upon nerve fibres, reaching the glands from the 

 lower dorsal and upper lumbar portions of the sympathetic chain. 

 The splanchnics form the most important path. When in the cat 

 the fibres coming to a semilunar ganglion from the sympathetic, 

 including the splanchnics, are cut, the secretion of epinephrin by 

 the corresponding adrenal into the blood comes at once to an end. 

 It is not resumed when the animal is allowed to survive. When 

 the peripheral ends of the cut splanchnics are stimulated electrically, 

 secretion is caused, and the amount of epinephrin discharged per 

 minute may exceed that spontaneously liberated (Figs. 212, 213). 



This was first indicated by the experiments of Dreyer, who col- 

 lected blood from the adrenal vein of a dog during splanchnic stimu- 

 lation, and caused a rise of blood-pressure in another dog by injecting 

 the blood. The effect of stimulation of the splanchnic can be de- 

 monstrated very clearly by the eye reactions already alluded to. 

 After the interval required for the blood to pass from the adrenals 

 to the eye, dilatation of the pupil and retraction of the nictitating 

 membrane are seen to occur. In this way it has been shown that 



