564 A MANUAL OF PHYSIOLOGY 



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 in- 

 crease of blood-pressure. The generalization may be made 

 that suprarenal extract or adrenalin, 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 pro- 

 nounced 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 in- 

 different 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 

 ' receptive ' substance at the myoneural junction. Thus adrenalin 

 causes marked diminution of tone in the small intestine, with 

 disappearance of the peristalsis and pendulum movements. 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 even in a dilution of I : 1,000,000. A similar 

 action has been observed on the stomach. The vessels of the 

 conjunctiva are constricted by local action when an extract of 

 the capsules is dropped into the eye, a fact which has proved of 

 value in ophthalmological practice. Inhibition of the con- 

 traction of the stomach, intestine, urinary bladder, and gall- 

 bladder ; contraction of the uterus, vas deferens, and seminal 

 vesicles ; dilatation of the pupil and retraction of the nictitating 

 membrane ; stimulation of the salivary and lachrymal secre- 

 tions, are among its actions (Langley). The curve of con- 

 traction of the skeletal muscles is lengthened as in veratrine 

 poisoning (p. 654), though to a less extent. Adrenalin or 

 suprarenin (C 9 H 13 NO 3 ) is solely contained in the medulla of 

 the gland, and such is its extraordinary power, that a dose 

 of one - millionth of a gramme per kilo of body - weight is 

 sufficient to cause a distinct effect upon the heart and blood- 

 vessels (a rise of pressure of 14 millimetres Hg). Another 

 delicate, and for certain purposes a convenient, reaction for 

 the detection and the physiological assay of adrenalin is the 



