REGULATORS 593 



of the pancreas may inhibit the action of adrenalin on these 

 terminations. 



(7) It acts on the sweat glands, which are supplied by the 

 true sympathetic nerves, but its action is masked by the 

 constriction of the vessels which supply these glands. 



(8) On the kidney its constricting action on the arterioles leads 

 to a decreased production of urine. 



(9) As already indicated (p. 356), injections of extracts of 

 the suprarenal bodies profoundly modify the metabolism, leading 

 to an increase of sugar in the blood and to its excretion in the 

 urine. This is best marked when the animal is well fed and 

 has a store of glycogen in its liver ; but, since it occurs in 

 fasting animals, after the stored carbohydrates have been 

 markedly reduced by the administration of phloridzin (p. 357), 

 it would appear to be due in part to an increased production of 

 sugar from proteins. It has been suggested that the supra- 

 renal secretion acts through the pancreas by preventing the 

 formation of the internal secretion which checks carbohydrate 

 metabolism in the liver (see p. 356). But the fact that it 

 produces glycosuria in the bird after the pancreas has been 

 excised negatives this view. The universality of the law that 

 adrenalin acts on the terminations of true sympathetic nerves, 

 and the fact that stimulation of these nerves to the liver causes 

 a glycosuria, indicates that it probably acts on these nerve 

 endings. This is supported by the fact that it does not cause 

 glycosuria after the administration of ergotoxin. 



4. Nervous Control of the Chromaffin Tissue. — The supply of 

 adrenalin to the body from the chromaffin tissue is influenced 

 by the nervous system through the splanchnic nerves, pregan- 

 glionic medullated fibres of which go to the gland. Various 

 injuries to the central nervous system may stimulate these 

 nerves, and a glycosuria may be thus produced, as in Bernard's 

 diabetic puncture (p. 356). Since this does not occur when the 

 suprarenals are removed, it has been supposed that it is caused 

 by the excessive supply of adrenalin to the blood. But the 

 amount in the blood after Bernard's puncture is insufficient to 

 cause a glycosuria. The adrenalin probably acts merely as an 

 adjuvant to nerves. 



5. Significance of Adrenalin. — The amount of adrenalin 



normally present in the blood is quite insufficient to exercise 

 38 



