882 PHYSIOLOGY OF DIGESTION AND SECRETION. 



pathological lesions in the suprarenal capsules. These older ob- 

 servations indicated clearly enough that the adrenal glands are of 

 essential importance to the life of the organism, but the first precise 

 indication as to the nature of its activity was furnished by the dis- 

 covery, made by Oliver and Schafer,* of the remarkable effects 

 observed when an extract of the medulla of the gland is injected 

 into the circulation of a living animal. Briefly stated, the effect 

 of such an injection is a pronounced slowing of the heart-beat 

 together with a rise of pressure. The slowing of the heart-beat is 

 due to a stimulation of the cardio-inhibitory center, for if the 

 vagi are cut before making the injection this result drops out; 

 the blood-pressure, on the contrary, not being restrained by the 

 slowing of the heart, rises rapidly and may reach an extraordinary 

 height. The explanation of the effect of the extracts on blood- 

 pressure is given below. 



Since effects of this kind were not obtained from extracts of the 

 cortex of the gland, it was apparent from these initial experiments 

 that in the adrenal, as in the thyroid tissue, there are two organs 

 or tissues to be considered whose functions may be very different. 

 Subsequent investigations have served to strengthen this belief, f 

 The cortical and medullary tissues are separate anatomically from 

 each other in some of the fishes, and embryologically have different 

 origins. It has been proposed to speak of the cortical tissue as the 

 interrenal system and of the medulla as the adrenal or the chro- 

 ma ffin or chromaphil system, but for our purpose it will be simpler 

 to state briefly the main facts that have been obtained under the 

 headings cortex and medulla. 



Physiology of the Medulla. The Active Principle, Epinephrin. 

 Chemical investigations of the substance in the medulla which 

 causes the inhibition of the heart and the rise of blood-pressure 

 have been very successful. The substance has been prepared in 

 pure form, its chemical structure is known, and it has been made 

 synthetically outside the body. J The credit for the most impor- 

 tant initial work is due to Abel, while the final isolation in pure form 

 as crystals was accomplished by Takamine and independently by 

 Aldrich. The last-named observer determined the correct formula 

 for the active substance, namely, C 9 Hi 3 NO 3 , and later workers 

 (Stolz and Dakin) succeeded in demonstrating its chemical struc- 

 ture as a dioxyphenyl ethylol-methylamin, C 6 H 3 (OH) 2 CHOH- 

 CH 2 NHCH 3 . The presence of the oxyphenyl group in the com- 

 pound would suggest that in the body it is probably derived from 



* Oliver and Schafer, "Journal of Physiology," 18, 230, 1895. 



t See Swale Vincent, " Transactions of the American Gynecological So- 

 ciety, 1917. 



JFor description of chemistry and references, see Barger, "The Simpler 

 Natural Bases" (Monographs on Biochemistry), 1814. 



