THE SUPRARENAL SYSTEM 183 



tion of 1:1,500,000. Pure urine frequently gives a similar 

 positive reaction, and Schur thinks it possible that adrenalin is 

 one of the constituents of normal urine. The sensibility of this 

 iodine reaction may also be made use of in quantitative adrenalin 

 tests. 



The biological methods employed for the detection of adren- 

 alin will be discussed later. 



THE PHYSIOLOGICAL ACTIVITY OF ADRENALIN. 



Of the physiological effects of adrenalin, that which it exer- 

 cises upon the vascular apparatus is the most important and the 

 most characteristic. This is readily seen if a certain quantity 

 (about one-twentieth mg.) of adrenalin is injected into the veins 

 of an animal, and its blood-pressure registered by means of a 

 kymograph. The injection is followed almost immediately by 

 a rapid increase in blood-pressure which rises to a considerable 

 height, but this is partly concealed by the fact that, soon after 

 injection, the pulse becomes extremely slow. The increase in 

 blood-pressure lasts a short time only, from thirty seconds to two 

 to three minutes according to the dose, and the maximum is 

 obtained for a few seconds only. The retardation of the pulse 

 soon disappears also, and is followed by a gradual fall in 

 pressure, the starting point being reached in two, or at the most 

 four, minutes. 



The increase in pressure is very much more perceptible if the 

 fall in the pulse-rate is avoided. This is done by eliminating, by 

 means either of atropine or resection, the inhibitory influence 

 of the vagi upon the cardiac contractions. If this is done, the 

 blood-pressure rises to twice, or even three times, the normal 

 figure. Blood-pressures reaching 250 to 300 mm. Hg. may by 

 this means be observed in dogs and rabbits, figures which are 

 not obtainable by the action of any other substance. Where 

 breathing is spontaneous, the respiratory fluctuations in blood- 

 pressure disappear during the rise and while the tension is at 

 its height ; they reappear as the tension gradually diminishes. 



A rise in blood-pressure follows the exhibition of even 

 minimal doses ; the amount of the increase and its duration are 

 to a certain extent proportional to the amount of substance 

 injected. A typical increase in pressure of about 15 to 25 mm. 

 Hg. is obtainable with .0005 mg., and is certain with .001 mg., 

 to every kilo of body-weight, of both the natural adrenalin and 

 the synthetic suprarenin. A dose of .005 mg. will raise the blood- 

 pressure 50 mm. Hg. ; and after .01 mg. it may be increased by 

 as much as 80 to 100 mm. Hg. An increase in the dose gradually 

 prolongs the period of hypertension. The maximal degree of 

 pressure is usually obtainable with .1 mg. adrenalin, while a 

 further increase of two to tenfold in the amount of the dose 



