886 PHYSIOLOGY OF DIGESTION AND SECRETION. 



distinct toxic effect. The lethal dose varies with the animal used 

 and the mode of administration. When given intravenously 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 hemorrhages 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 than in this case there is 

 a primary constriction due to the action of the vasomotor fibers, 

 but this is followed and sustained 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, 

 such as the dilatation of the pupil in an excised eye of the frog 

 (Meltzer reaction), the contraction of rings of arteries (Meyer's 

 test), or the relaxation of strips of intestine (Cannon-Hoskin), all 

 agree in indicating that the venous blood flowing from the adrenal 

 gland contains epinephrin. The amount is small, so small that 

 attempts to demonstrate its existence in the general circulation 



* Dreyer, "American Journal of Physiology," 2, 283, 1899. 



