108 MEDULLA 



Heymans 297 also, on the basis of his experiments on the 

 carotid sinus, considered the adrenals as playing an important 

 role in regulating the cardiac rate and blood pressure. The 

 carotid sinus according to Heymans reflexly regulates the 

 vagal cardiac tone, the neuro-vascular tone, and the secretion 

 of epinephrine from the adrenals. Changes in these functions 

 take place in response to alterations in the blood pressure to 

 which the carotid sinus is exceedingly sensitive. In Heymans' 

 experiments the carotid artery of a dog, B, whose carotid sinus 

 had been isolated, was anastomosed to the jugular vein of a dog, 

 A. The lumbo-adrenal vein of B was in turn anastomosed with 

 the jugular vein of a third dog, C, whose adrenals had been 

 extirpated. Changes in the volume of the spleen of dog C 

 served to detect epinephrine secreted by dog B in response 

 to changes in the blood pressure of its carotid sinus. A drop 

 in the arterial blood pressure of the sinus of B, called forth 

 vasoconstriction and a reflex stimulation of epinephrine secre- 

 tion in this animal, while a rise in pressure resulted in vaso- 

 dilation and an inhibition of epinephrine secretion. 



As pointed out by Cannon, 103 the disturbed experimental 

 conditions of the above quoted experiments deprive them of 

 their validity. The abnormally excessive amounts of epineph- 

 rine secreted under the experimental conditions cited undoub- 

 tedly affect the circulation. The amounts secreted in the 

 normal resting animal, however, could exert no such profound 

 effects. Cannon and his collaborators in their studies of quiet 

 unanesthetized cats, with hearts denervated for some time, 

 could detect no difference between the basal pulse rate before 

 and after exclusion of the secretion of the adrenal medulla by 

 denervation or excision of these glands. 



Because of the remarkable pharmacological effects elicited 

 by epinephrine when injected into the blood stream, numerous 

 theories have been suggested to explain a variety of clinical 

 conditions as being dependent on pathological changes in the 

 medulla. The hyperglycemic action of epinephrine led 



