878 PHYSIOLOGY OF DIGESTION AND SECRETION. 



seem to indicate that the normal secretion of epinephrin may play 

 a part in the complex sugar-regulating mechanism of the body, 

 and there is evidence, which will be referred to briefly later, that 

 the other glands of internal secretion, or some of them at any rate, 

 are also concerned in the regulation of the sugar supply and sugar 

 consumption. When administered in large doses epinephrin has a 

 distinct or even fatal toxic effect. The lethal dose varies with the 

 animal used and the mode of administration. When given intra- 

 venously a dose of as much as 1 mgrm. per kilogram of body 

 weight may be followed by a rapid paralysis of respiration or of the 

 heart, or by a more gradual intoxication accompanied by hemor- 

 rhages from the intestinal mucosa. 



The Secretory Nerves of the Adrenal Gland. The adrenal glands 

 receive a supply of sympathetic autonomic nerve-fibers by way of 

 the splanchnic nerves. Dreyer* first demonstrated that the produc- 

 tion of epinephrin in the gland may be increased upon stimulation 

 of these fibers and that in all probability the output of epinephrin 

 is regulated through definite secretory fibers. This conclusion has 

 been corroborated by more recent work. Sensory stimulations of 

 various kinds, strong emotional excitement, and other conditions 

 seem to cause a reflex stimulation of the gland and a consequent in- 

 crease in the concentration of epinephrin in the blood. In fact, it 

 would appear that some of the variations in arterial pressure, which 

 have been explained heretofore as the immediate result of direct or 

 reflex stimulation of vasoconstrictor fibers, may be due rather to a 

 reflex stimulation of the adrenal glands which brings about a vaso- 

 constriction through an increased amount of epinephrin. When 

 the splanchnic nerves (peripheral end) are stimulated, for example, 

 a marked vasoconstriction is produced throughout the so-called 

 splanchnic area. Analysis seems to show that in this case there is a 

 primary construction due to the action of the vasomotor fibers, 

 but this is followed by an additional constriction caused by the 

 increased output of epinephrin. 



The Functional Significance of the Medullary Tissue. The 

 normal functional value of the medullary tissue and of the other 

 chromaffin tissues consists, so far as we know, in the production and 

 secretion of epinephrin, and discussions upon this question have 

 centered, therefore, upon the normal occurrence and significance 

 of the epinephrin. Examination of the venous blood flowing from 

 the adrenal gland discloses the fact that it contains epinephrin. 

 The presence of the base is shown most satisfactorily by its physio- 

 logical reactions. When the blood from the adrenal vein is col- 

 lected and injected into another animal it produces the character- 

 istic epinephrin effect upon blood-pressure; other similar tests, 

 * Dreyer, "American Journal of Physiology," 2, 203, 1899. 



