SECRETION OF THE DUCTLESS GLANDS. 879 



such as the dilatation of the pupil in an excised eye of the frog 

 (Meltzer reaction), the contraction of rings of arteries (Meyer's 

 test), or the relaxation of strips of intestine (Cannon-Hoskin), all 

 agree in indicating that the venous blood flowing from the adrenal 

 gland contains epinephrin. The amount is small, so small that 

 attempts to demonstrate its existence in the general circulation 

 have not been entirely satisfactory; some claim to have shown its 

 presence, while others get negative results. It is generally believed, 

 however, that the blood does receive constantly a supply of epi- 

 nephrin from the adrenal glands and that this constitutes the inter- 

 nal secretion of the medullary cells. As regards the function of the 

 epinephrin under normal conditions there is some difference of 

 opinion. The usual view is that it serves to maintain a condition 

 of tonicity in the musculature of the heart and blood-vessels inner- 

 vated by the sympathetic autonomic system and thus insures a 

 normal cardiovascular tone. If the amount of epinephrin falls 

 below normal or fails entirely, a condition of hypotension results in 

 consequence of general vascular dilatation. When epinephrin is 

 secreted in excess the opposite condition of hypertension prevails. 

 This theory is insufficient in that it does not take into account the 

 other physiological reactions of epinephrin, such as the effect on car- 

 bohydrate metabolism, and, moreover, it is not entirely in accord 

 with some observations upon the results of removal of the adrenal 

 glands. In spite of the large amount of experimental work upon 

 the action of epinephrin, it seems necessary at present to recognize 

 the fact that our knowledge is too incomplete to justify any posi- 

 tive statements in regard to its normal role in the organism. 



As stated above, the rise of blood-pressure and the slow heart- 

 beat caused by injections of epinephrin last but a few minutes. 

 Apparently the excess above the normal concentration in the blood 

 is quickly destroyed in some way. Possibly it is absorbed and oxi- 

 dized or otherwise changes by the tissues, but on this point also 

 experiments as yet have not given a decisive result.* 



The Functional Significance of the Cortical Tissue. Most ob- 

 servers agree that the cortex does not contain epinephrin, and it is 

 probable, therefore, that its functions are different from those of 

 the medulla. Biedl has shown that in those fishes in which the 

 cortical substance exists as a separate structure, the interrenal body, 

 extirpation of this organ is followed by a condition of progressive 

 muscular weakness ending in death. This result would indicate 

 that the cortical tissues have some specific and essential internal 

 secretion, and it would seem possible, moreover, that the fatal result 

 always following extirpation of the adrenal bodies is due to loss of 

 the cortical rather than the medullary substance. Some experi- 

 * For general reviews of literature, consult Biedl, "Innere Sekretion," 1913. 



