786 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



That epinephrine is being constantly liberated in certain minute 

 amounts is probably true, but whether this amount is a factor in the 

 maintenance of normal arterial tone, or is concerned in lowering the 

 resistance of the sympathetic endings, is another question. Experimental 

 investigation does not sustain the so-called "tonus" hypothesis. In the 

 first place, in the experiments already cited (page 785), the amount of 

 epinephrine secreted spontaneously would be, when diluted with the mass 

 of blood of the entire circulation, quite inadequate to have any effect 

 upon blood pressure; in the second place if any effect upon the vessels 

 did occur with these minute doses it would be one not of constriction 

 but of dilatation, on many vessels at least (page 777). No effects were 

 observed on the general health or the blood pressure of animals in 

 which the adrenal of one side was removed, and the nerve control of the 

 opposite gland severed, although under the conditions it is evident 

 that very little epinephrine could have been present in the blood (not 

 more than 1 part in 400 million parts of blood). Experiments performed 

 by Vincent and others gave similar results. Hoskins and McClure 24 at- 

 tacked the problem in a different way, but arrived at a like conclusion. 

 They found that the amount of injected epinephrine necessary for the pro- 

 duction of a certain predetermined response was, after adrenalectomy, 

 but slightly in excess of that required to be injected into the same ani- 

 mal with intact glands. This excess, which represented the tonic secre- 

 tion of the glands, was far below the threshold for vasoconstrictor stim- 

 ulation. Finally, epinephrine is not present in the sera of patients suf- 

 fering from vascular hypertonus in sufficient concentration to be detected 

 by any of the biological tests at our disposal. (Stewart.) 25 



Since the "tonus" hypothesis of the adrenal function is untenable, 

 another, or emergency hypothesis has been brought forward. According 

 to this, epinephrine is considered to be secreted into the blood in super- 

 normal amounts when certain emergencies arise, such as asphyxia or con- 

 ditions of extreme emotion such as fright or fear. An experimental hy- 

 persecretion of an analogous character is also said to occur during stimu- 

 lation of the central end of large sensory nerves such as the sciatic. 

 The chief exponent of this hypothesis is Cannon, 26 and he has supported 

 it by a seemingly incontrovertible mass of experimental evidence. In the 

 earlier researches which appeared in 1911 the blood was removed from the 

 vena cava opposite the openings of the adrenal veins, by pushing a cath- 

 eter up to this level through a slit in the femoral vein, and blood was 

 tested for the presence of epinephrine by observing its effect on the 

 beating of an isolated strip of intestine. It was found that whereas the 

 blood of a normal male cat did not give evidence of the presence of epine- 

 phrine, it did so in a cat that had previously been frightened by allowing a 

 dog to bark at it. Such results were not obtained after the removal of the 



