SECRETION OF THE DUCTLESS GLANDS. 875 



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, 

 according to some authors, cause a reflex stimulation of the gland 

 and a consequent increase in the concentration of epinephrin in 

 the blood, but other observers maintain that while such a reflex 

 excitation of the gland might be expected because of the existence 

 of the secretory fibers, the actual experimental demonstration 

 has not been obtained. On account of this uncertainty the various 

 attempts made in physiological and pathological literature to ex- 

 plain certain reactions as due to an increased output of epinephrin 

 from the adrenal glands must be accepted with some caution. 



The Functional Significance of the Medullary Tissue. — The 

 normal functional value of the medullary tissue and of the other 

 chromaflSn 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. According to 

 Stewart and Rogoft'f it amounts in cats to 0.0003 to 0.001 mg. 

 per kilo per minute. Whether or not epinephrin is present in the 

 general circulation is doubtful. If present the concentration is so 

 small that the available tests for epinephrin fail to give a decisive 



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

 t Stewart and Rogoff, "Journal of Exp. Med.," 26, 613, 1917. 



