THE SUPRARENAL SYSTEM 147 



which rendered the suprarenals necessary to life, seemed at first to 

 have already received an answer. The specific physiological effects 

 of suprarenal extract, to which we shall refer later, were known. It 

 was also known, or at any rate suspected, that the active principle 

 of the extract was derived from the medullary substance, and that 

 this essence passes intra vitam into the blood-stream by way 

 of the suprarenal veins. 



In view of the known physiological activity of the medullary 

 substance, the conclusion seemed obvious that animals from 

 which both suprarenals had been removed, died from the lack of 

 an essence, elaborated by the suprarenal medulla, which is neces- 

 sary to the performance of a large number of bodily functions. 

 According to Cybulski, this essence maintains in a state of 

 normal tonus, the activity of those nervous centres which control 

 the cardiac and vascular muscles, the respiratory musculature r 

 and perhaps the muscular tissue of the entire body. After re- 

 moval of the suprarenals the animal dies, because, in the absence 

 of perpetual stimulus, these nerve centres, the activity of which 

 is essential to the life of the organism, cease to act. 

 The evidence in support of this theory is that, in dying animals 

 from which the suprarenals have been removed, the blood- 

 pressure is extremely low, while interference with respiration, as 

 by occlusion of the trachea, does not produce either a dyspnceic 

 increase in blood-pressure nor dyspnceic cramps. The injection 

 of suprarenal extract is followed by an increase in blood-pressure 

 accompanied by a certain improvement in vitality, and the 

 dyspnceic blood produces the usual symptoms of suffocation. 



These experiments have no great value as evidence, especially 

 when we consider that, in all moribund animals, there is a low 

 arterial blood-pressure and a slight reaction to dyspnceic stimuli, 

 and that the injection of suprarenal extract into moribund animals 

 is always followed by a rise in blood-pressure and a certain return 

 of vitality. 



What seems to be more reliable proof of the part played by 

 the medullary substance in death from suprarenal suppression, 

 is the fact that extirpation of both suprarenals is immediately 

 followed by a considerable reduction in arterial tension. Strehl 

 and Weiss attribute this fall in blood-pressure to the cessation 

 of the supply of the substance which stimulates blood-pressure. 

 Their views are founded upon the results of the following experi- 

 ment with rabbits. 



If, after removal of one suprarenal, the vein leading from 

 the other is severed or ligatured, in certain cases, " though in a 

 small minority only," there will be a marked fall in blood-pressure. 

 If the ligature is released, the blood-pressure will rise to the 

 normal. Young and Lehmann performed a similar experiment 

 upon dogs; they found that the ligature of both suprarenals 

 gradually produced a slight reduction in arterial pressure, and 



