60 



held up by the ears will die ; the wild rabbit 

 survives. In the tame animal, all the blood tends 

 to collect in the pendulous belly, and the feeble vaso- 

 motor control is unable to constrict the vessels and to 

 drive it up to the brain. This picture is very similar 

 to that of surgical shock in man. 



There is yet another governing factor, and, we 

 must believe, an essential one. The suprarenal 

 glands are constantly pouring into the blood their 

 internal secretion, which we know as adrenalin. The 

 medulla of the suprarenal glands is developed from 

 the sympathetic nervous system, and adrenalin is 

 essential for the proper action of all the motor nerve 

 endings of that system. Injection of adrenalin 

 produces all the effects on involuntary muscle that 

 are characteristic of stimulating the sympathetic, 

 and some of the effects on glandular secretion. Yet 

 it does not act by stimulating these nerve endings 

 themselves, because it continues to produce its action 

 after section and degeneration of sympathetic nerves. 

 The most prominent of its effects is a powerful but 

 transient vasoconstriction. 



That adrenalin is being poured out continually to 

 maintain the activity of the vasoconstrictors we 

 know by research along two distinct lines of 

 access. If the suprarenal veins are clamped for 

 a few hours, the blood-pressure falls. On their 

 release the accumulated adrenalin passes into the 

 circulation, and the blood-pressure rises rapidly 

 above normal. 



Further light is shed upon the matter by a study 

 of the phenomena of Addison's disease, in which the 



