638 INTERNAL SECRETION 



'bronzing' of the skin, are prominent symptom sj was associated 

 with disease, usually tuberculous, of the adrenal bodies, commonly 

 called in human anatomy the ' suprarenal capsules.' This clinical 

 result was soon supplemented by the discovery thatfextirpation of 

 the adrenals in animals is incompatible with HfeJ(Brown-Sequard). 

 Our knowledge of the functions of these hitherto enigmatic organs 

 was extended by the experiments of Oliver and Schafer, who in- 

 vestigated |t he action of extracts of the adrenals (of calf, sheep, 

 dog, guinea-pig, and man) when injected into the veins of animals. 

 The arteries are greatly contracted) and this mainly through direct 

 action on the vaso-motor nerve-endings or some structure inter- 

 mediate between them and the smooth muscle of the vessels, but 

 partly through the vaso-motor centre, fThe blood-pressure rises 

 rapidly, although the heart may be inhibited through the vagus 

 centre.l The heart is at the same time directly stimulated, so that, 

 although it beats slowly, the beats are stronger than before. When 

 the vagi are cut the action of the heart is markedly augmented, 

 and the arterial pressure rises enormously (it may be to four or five 

 times its original amount). Stimulation of the depressor is of no 

 avail in combating this increase of blood-pressure. The generaliza- 

 tion may be made that suprarenal extract or adrenalin also called 

 ' epinephrin ' and ' suprarenin ' its active principle, acts upon all 

 plain muscle and gland-cells that are supplied with sympathetic 

 nerve-fibres, and the result of the action, whether augmentation 

 or inhibition, is the same as would be produced by stimulation of 

 the sympathetic fibres going to the muscle or gland in question. 

 Yet it is not through excitation of these fibres that the adrenalin 

 acts, for its effect is even more pronounced when the nerve-fibres 

 have been caused to degenerate, in the case of the pupillo- dilator 

 fibres, e.g., by excision of the superior cervical ganglion. Nor is the 

 effect a direct one on the muscular fibres. For smooth muscle which 

 is not, and never has been, in functional union with sympathetic 

 nerve-fibres is indifferent to adrenalin (Elliott). It seems, then, 

 to act on some structure intermediate between the nerve and the 

 muscle, but so related to the latter that it continues to live so long 

 as it is in connection with the muscle-fibre. Instead of a definite 

 histological structure, the seat of the action may be a special ' re- 

 ceptive ' substance at the myoneural junction. |Thus adrenalin 

 causes marked diminution of tone in the small intestine, with dis- 

 appearance of the peristalsis and pendulum movements. J The same 

 effect is produced on an isolated loop of intestine immersed in 

 Locke's solution, and the action is therefore local. The drug is 

 effective in a dilution of i : 1,000,000, or even in much greater dilution. 

 A. similar effect has been observed on the stomach^ fThe vessels 

 of the conjunctiva are constricted by local action when an extract 

 of the capsules is dropped into the eyela fact which has proved of 



