872 PHYSIOLOGY OF DIGESTION AND SECRETION. 



tyrosin. This active substance is designated in the hteratiire 

 under a variety of names, those commonly used being epinephrin, 

 adrenahn, and adrenin. It is a basic body which gives a number of 

 characteristic color reactions, and in alkaline solutions is readily 

 oxidized to a substance that fails to exhibit the characteristic epi- 

 nephrin reaction on heart-rate and blood-pressure. 



The Chromaffin Tissues. — As stated above, the epinephrin 

 occurs in the adrenal gland in the cells of the medulla, but not in 

 those of the cortex. When the medullary cells are treated with 

 chromates they give a characteristic yellow or brown reaction, 

 which is spoken of as a chromaffin reaction and has been used to 

 locate similar cells in other tissues. It would seem that cells of 

 this variety may be found generally or frequently in the sym- 

 pathetic ganglia, so that it has been suggested that primitively 

 each such ganglion contained two varieties of cells, the nei-ve 

 cell or gangUon cell and the chromaffin or paraganglion (Elhott) 

 cell. Clumps or strings of such cells occur also along the course of 

 the abdominal aorta below the level of the adrenal glands, and, as 

 was stated above, in some of the fishes the medullary cells of the 

 adrenal gland are separated anatomically from the cortical cells. 

 On account of the color reaction and the demonstration, in some 

 cases at least, that this color reaction indicates the presence of 

 epinephrin, it has become customary to group all the cells exhibit- 

 ing the chromate reaction under the general term of chromaffin or 

 chromaphil system* and to suppose that all this tissue, wherever 

 found, has a common physiological significance. The medulla of 

 the adrenal gland is the most conspicuous and important group of 

 these cells, but it is assumed that in case of removal by disease or 

 experiment its functions may be supplied more or less perfectly 

 by the outlying cells belonging to the same tissue. 



Physiological Action of the Epinephrin. — As stated above, 

 solutions of epinephrin give a marked effect upon the heart-rate 

 and blood-pressure. The great slowing of the heart-rate is due to 

 an action of the epinephrin on the cardio-inhibitory center, since 

 it disappears when the vagi are cut or after the administration of 

 atropin. When this influence of the cardio-inhibitory center is 

 removed it can be shown that the epinephrin causes a stronger and 

 more rapid contraction of the heart, and a similar effect can be ob- 

 tained upon the isolated heart maintained by an artificial circula- 

 tion. It seems probable that this effect of the epinephrin is due to 

 a stimulating action upon the endings of the accelerator nerve in 

 the heart. In addition to the heart effect the epinephrin causes a 

 strong contraction of the arterioles in certain areas, and experiments 

 demonstrate that this effect is due mainly to a peripheral action. It 

 * See Vincent, "Proceedings of the Royal Society," B, 82, 502, 1910. 



