THE ADRENAL BODIES 973 



statement, however, is not intended to imply that the tonus of the 

 vascular system depends exclusively upon the presence of adrenin in 

 the blood-stream. Such an assertion cannot be correct, because the 

 walls of the blood-vessels are -already tonically set by virtue of the tonic- 

 ity resident in all living cells, and all the adrenin can do is to vary 

 their tonus. The fact that adrenin is liberated at a definite rate may 

 be proved by applying a temporary ligature to the suprarenal vein. 

 Very shortly after this obstruction to the venous return has been re- 

 moved, the blood pressure invariably shows an abrupt rise which 

 indicates that a certain amount of the accumulated adrenin has 

 reached the general circulatory system. Very similar results may be 

 obtained by temporarily blocking the inferior vena cava centrally to 

 the orifices of the suprarenal veins. Whenever the blood is then 

 allowed to escape from this pocket, the arterial pressure rises, again 

 proving that this stagnated cava blood has been charged with adrenin. 

 Under ordinary conditions, however, the amount of this '' spontane- 

 ously" hberated adrenin. is very small. Thus, Stewart and Rogoff^ 

 estimate it in cats at only 0.001 gram per minute. If this amount is 

 added to the blood of the general circuits, it will be seen that its con- 

 centration must be diminished so as to render it practically ineffective. 

 Actual changes in the circulation, therefore, can only occur when its 

 discharge is increased by stimulation. 



The adrenalin or adrenin introduced into the circulation, is 

 oxidized very soon after it has performed its temporary excitatory 

 action. This instability also accounts for its rapid disappearance from 

 food, so that perfectly enormous doses of it must be administered by 

 mouth before it can produce its effect upon the blood pressure. Certain 

 substances, however, have been isolated from the amino-acids by a 

 process of decarboxylation which, although similar in their composi- 

 tion to adrenalin, possess a much greater stabihty. Some of these 

 form the active principle of ergot. Adrenalin applied locally to 

 open surfaces constricts the blood-vessels and may therefore be em- 

 ployed as a means to stop excessive hemorrhagic oozing. When added 

 to solutions of sodium chlorid used for purposes of infusion, it acts 

 as a vasoconstrictor agent, thereby raising the blood pressure and pro- 

 ducing a stimulation of the heart by establishing a much greater per- 

 ipheral resistance than could be obtained with the sodium chlorid 

 alone. 



The Innervation of the Adrenal Bodies. — The activity of the 

 adrenal glands, at least of their medullary portions, is controlled by 

 nerve fibers which are derived from the greater splanchnic nerves. 

 Thus, BiedP and Dreyer^ have shown that the stimulation of this 

 nerve, or of its distal end, gives rise to a copious discharge of adrenin 

 which, upon reaching the distant arterial system, constricts these 



1 Jour. Exp. Med., xxiv, 1916, 709. 



2 Pfluger's Archiv, Ixvii, 1897, 443. 



3 Am. Jour, of Physiol., ii, 1899, 283. 



