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TEXT-BOOK OF PHYSIOLOGY 



but which is intimately related to the muscle. To this material Langley 

 has applied the term "receptive substance." In all instances the adrenalin 

 stimulates the receptive substances as a result of which the normal effect 

 produced by the sympathetic nerve impulse is intensified. 



The Influence of the Nerve System. The secretory activity of the 

 adrenals is regulated by the nerve system. Thus Dreyer found that the blood 

 of the adrenal vein after stimulation of the splanchnics was capab le of causing 

 to a much greater extent the usual physiologic effects when injected into an 

 animal than blood of the adrenal vein before stimulation and this independ- 

 ent of the vascular changes that were simultaneously provoked. It has also 

 been shown by Ascher that a high blood-pressure can be maintained by 

 prolonged stimulation of the splanchnics. Cannon has reported that major 

 emotional disturbances such as fright lead to an increase in the secretion 

 of the adrenals as shown by the fact that the blood taken from the vena cava 

 above the level of the adrenal veins will promptly produce an inhibition 

 of a contracting intestinal strip, while blood taken from the animal previous 

 to the fright, had no such effect. After ligation of the veins or the removal 

 of the adrenals there was a failure of this effect upon excitement. 



Emotional excitement in cats at least is also attended with hypergly- 

 cemia and glycosuria which is probably due to an increase of the adrenal 

 secretion in the blood inasmuch as .a similar effect follows the injection of the 

 extract into the blood. The hyperglycemia and glycosuria caused either 

 by the intravenous injection of the extract or by an increased activity of the 

 adrenals following emotional excitement, fear or rage, is difficult of explana- 

 tion. It may be the result of a direct action or an indirect action through 

 secretor nerves on the liver cells, in consequence of which the stored glycogen 

 is rapidly transformed into sugar and discharged into the blood. 



An advantage that would accrue to the animal from the accumulation 

 of sugar in the blood under these circumstances, would be a quickly avail- 

 able source of energy-yielding material, for the continued muscle activity 

 that would attend either flight or defense. 



The Function of the Adrenal Gland. The function of the adrenal 

 gland, at least of the medullary portion, is to furnish an internal secretion 

 which serves apparently to stimulate the receptive substance at the myo- 

 neural junction and thus cooperates .with the sympathetic system to maintain 

 that degree of frequency and force of the heart-beat and the contraction of 

 the arteriole muscle necessary to maintain the normal blood-pressure; to 

 inhibit as occasion requires, the tonus of muscle walls of various viscera; 

 to cause a mobilization of sugar in the blood when this is necessary, and 

 to increase in some unexplained way the tonus and activity of the skeletal 

 musculature. 



The Chromaphil Tissue. The chromaphil tissue lying along the aorta 

 and in other situations as well that portion of the original embryonic 

 chromaphil tissue that was not incorporated in the medulla of the adrenal 

 gland has been shown to possess physiologic actions similar to, if not 

 identical with extracts of the adrenal medulla itself. Thus it causes not only 

 a marked rise of blood-pressure but, according to the recent investigations of 

 Fulk and Macleod, in many mammals it inhibits the spontaneous contrac- 

 tions of isolated intestinal muscle and augments the tone and contractions of 

 the isolated virgin uterus. 



