656 INTERNAL SECRETION ENDOCRINE GLANDS 



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 ' receptive ' substance at the myo- 

 neural 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 in a dilution of 1 : 10,000,000, 

 or even in much greater dilution. A similar effect has been ob- 

 served on the stomach. The vessels of the conjunctiva are con- 

 stricted 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 contraction of the stomach, intestine, 

 urinary bladder, and gall-bladder; contraction of the uterus, vat 

 deferens, and seminal vesicles ; dilatation of the pupil and retraction 

 of the nictitating membrane ; stimulation of the salivary and lachry- 

 mal secretions, are among its actions (Langley) . 



Meltzer has shown that the dilatation of the pupil caused by the 

 intravenous injection of adrenalin is distinct, though fleeting, in cats, 

 less marked in rabbits. Subcutaneous injection has no effect. Instffia- 

 tion of the drug into the conjunctival sac is without effect on the pupil 

 in the normal rabbit's eye, but causes dilatation if the superior cervical 

 ganglion has been removed. 



The influence of adrenalin in increasing the sugar content of the 

 blood, and thus causing glycosuria, has been previously discussed 

 (p. 550). A new and interesting action has been added to the already 

 long list of the effects of adrenalin, by the discovery that small doses 

 (o'ooi milligramme per kilo of body-weight) injected intravenously, 

 and larger doses injected subcutaneously into cats shorten the coagula- 

 tion time of the blood to one-half or one-third of its previous duration, 

 probably by stimulating the liver to greater activity in discharging 

 some substance or substances concerned in clotting (Cannon). The 

 injection of adrenalin into the blood is said to cause a temporary im- 

 provement in the response to stimulation of a fatigued muscle still in 

 connection with the circulation, and this improvement does not seem 

 to be entirely due to augmentation of the blood flow (Gruber, Cannon 

 and Nice). 



Methods for the detection and the assay of epinephrin in the small 

 quantities in which it can only be supposed to be present in physio- 

 logical liquids have been based upon certain of these actions. Such, 

 for example, is the extraordinary power of this active principle 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 bloodvessels (a rise of 

 pressure of 14 millimetres of mercury) when injected into the veins 

 of a mammal. The reaction is rendered more constant, although less 

 delicate, when the brain is previously destroyed and the animal used 

 as a spinal preparation. In pithed cats the assay can be accurately 



