166 CORTEX 



stimulated by factors such as an increase in room temperature 

 or an injection of epinephrine. The respiratory rate in dogs 

 may drop to 5 or 6 per minute. Respiratory paralysis is the 

 immediate cause of death, for the heart continues to beat 

 after the cessation of respiration. 



CIRCULATION 



The circulatory system manifests no signs of dysfunction in 

 the early stages of adrenal insufficiency. The blood pressure 

 remains normal and there is no sign of cardiac decompensation. 



When the first clinical signs of insufficiency are evident, the 

 pulse rate becomes rapid and may be irregular. Later, when 

 the clinical symptoms of insufficiency become pronounced, the 

 pulse rate becomes slowed and often assumes an idioventricular 

 regular rhythm or an irregular rhythm with the manifestations 

 of some degree of heart block. 



Electrocardiographic studies by Nicholson and Soffer 471 

 demonstrated the existence in adrenalectomized dogs of a slow 

 auricular fibrillation. This would be expected to lead first to 

 a partial heart block and eventually to a complete block with 

 the assumption by the ventricle of its idiopathic rhythm. 

 This disturbance in cardiac function may be due to the eleva- 

 tion of the potassium content of the blood and the disturb- 

 ance in the normal potassium-calcium ionic ratio. Such a 

 disturbance would explain also the earlier observations of 

 Loewi and Gettwert 401 on the hearts of frogs dying of adrenal 

 insufficiency. 



The blood pressure does not fall appreciably until a short 

 time before death. The cardiac output, on the other hand, 

 according to Harrop et alii, 268 diminishes progressively after 

 the initiation of the first symptoms of insufficiency. This drop 

 in cardiac output may be looked upon as a reflection of the 

 decreased metabolic activity of the organism and not neces- 

 sarily indicative of cardiac insufficiency. 243 



Two chief factors are probably responsible for the circula- 



