ADRENALS 657 



performed to O'Ol milligramme. Another delicate, and for certain pur- 

 poses a convenient, reaction for the detection and the physiological 

 assay of epinephrin is the perfusion test on the legs of frogs already 

 alluded to (p. 46). The dilatation of the pupil in the excised eyeball 

 of the frog, the contraction of stretched artery rings (p. 66), the increase 

 in the tone of isolated segments of the uterus of rabbits, and the diminu- 

 tion in the tone of isolated segments of rabbits' intestine (Practical 

 Exercises, p. 453), have also been employed as physiological tests. 



A dilute solution of adrenalin chloride is used in medicine as a styptic, 

 and for reducing congestion in accessible parts. The intense local 

 anaemia which it causes when given subcutaneously or by the mouth 

 is one reason, perhaps the most important, for the 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. The striking effects produced by adrenalin 

 have naturally led to the assumption that the function of epinephrin 

 in the body must be important. But there is perhaps no chapter of 

 recent physiology in which the rash application of qualitative data to 

 what is essentially a quantitative problem has led to greater errors. 

 Because adrenalin in a certain amount and concentration raises the 

 blood-pressure when injected intravenously (a fact certainly of some 

 pharmacological interest), it has been assumed that the naturally 

 secreted epinephrin must be an important factor in the maintenance 

 of the normal vascular tone and arterial pressure. From this assump- 

 tion it was only a short step to the announcement that the blood in 

 cases with permanently increased blood-pressure (so-called arterial 

 hypertonus, etc.), and even the urine contained truly incredible con- 

 centrations of epinephrin. Because the injection of what in proportion 

 to the normal output of epinephrin must be designated as monstrous 

 doses of adrenalin causes an increase in the sugar of the blood and the 

 appearance of sugar in the urine, it has been supposed by many that all 

 the experimental hyperglycaemias and glycosurias (p. 547) are directly 

 due to increased liberation of epinephrin from the adrenals. The fallacy 

 of giving a physiological value to the details of the pharmacology and 

 toxicology of a substance produced in the body or known to exist in 

 the blood in the absence of information as to its amount and condition 

 would have been very evident in the case, for example, of ammonium 

 or potassium, and nobody would have dreamt that the effects produced 

 by massive injections of ammonium or potassium compounds of various 

 kinds would inform us of the role played by the ammonium and potas- 

 sium compounds circulating in normal blood. The whole question of 

 the function of epinephrin turns, therefore, upon the quantity wh'ch 

 can possibly be present in the systemic arteries or capillaries. Direct 

 assays of such blood by trustworthy observers using the most delicate 

 methods available have hitherto yielded negative results, both in health 

 and in disease. This is due to the great dilution and rapid removal 

 or oxidation of the epinephrin known to be given off by the adrenal 

 glands. 



That epinephrin is continuously liberated into the blood from the 

 adrenals is readily shown by tying off a long segment of the inferior 

 vena cava in such a way that only the adrenal veins discharge into it. 

 The cava pocket is temporarily clipped above the level of the orifices 

 of the adrenal veins and allowed to fill with adrenal blood. When the 

 blood is now released into the circulation by removing the clip, a rise 

 of blood-pressure (Fig. 208) is produced, beginning after an interval 

 sufficient for the blood from the pocket to pass round to the systemic 

 arterioles. Another method is to observe the effect of the released blood 



42 



