640 INTERNAL SECRETION 



slow absorption on which depends the absence of its general effects, 

 including that on the blood-pressure, when it is administered in 

 this way. 



Function of Epinephrin (or Adrenalin). The striking effects 

 produced by adrenalin have naturally led to the assumption that 

 its function in the body must be important. It has been con- 

 clusively proved that under certain conditions it is given off to the 

 blood, but only in such quantities as, when diluted by the general 

 mass of the blood, lie far below the concentration necessary for detec- 

 tion by any of the biological methods mentioned above. In fact, no 

 proof has ever been given that in blood withdrawn from an artery, 

 either in health or disease, adrenalin exists at all. When the 

 adrenal gland of a dog is directly massaged by the fingers, the blood 

 coming from the adrenal vein has been shown to contain a small 

 but detectable amount of adrenalin. The same is true of the blood 

 coming from the adrenal during stimulation of the splanchnic 

 nerves on the corresponding side (Fig. 206). 



The existence of secretory fibres for the adrenal glands in the 

 splanchnic nerves was first indicated by the experiments of Dreyer, 

 who found that the amount of active substance in the blood of the 

 suprarenal vein, as tested by its physiological effect when injected 

 into an animal, was increased by stimulation of those nerves. 



Under the influence of strong emotions, painful stimulation oi 

 sensory nerves, and other conditions, the quantity of adrenalin 

 which can be extracted from the adrenals is markedly diminished, 

 but not if the splanchnic fibres have been previously cut. 



That adrenalin is actually given off to the blood during stimula- 

 tion of a nervous mechanism of which the efferent fibres run in the 

 splanchnics is further indicated by facts like the following: Similar 

 changes in the clotting time of blood are produced by splanchnic 

 stimulation as by injection of adrenalin, and these changes do not 

 occur if the adrenal on the side of the stimulated nerve has been 

 previously excised. Excitation of afferent nerves under light 

 anaesthesia and emotional excitement also shorten the coagulation 

 time, but this effect is not obtained after section of the splanchnic 

 nerves. Temporary improvement in the response to stimulation 

 of a fatigued muscle, still in connection with the circulation, is 

 observed on excitation of the splanchnic nerve if the corresponding 

 adrenal is intact, and a similar reaction is obtained on injection 

 of epinephrin. 



The existence of a reflex nervous mechanism through which the 

 gland can be stimulated to secrete adrenalin into the blood can 

 therefore be considered as definitely established. But the function 

 of the adrenalin, once it has entered the circulation, is involved in 

 doubt. The common view is that it exerts an important physiological 

 action upon the sympathetic system, contributing especially to the 



