5 o8 TEXT-BOOK OF PHYSIOLOGY 



muscles that have been deprived of their nerve connections through degenera- 

 tive changes following division of the nerves, are influenced by adrenalin, 

 have led to the assumption that it acts neither on muscle nor nerve, but on 

 some material which intervenes between the nerve endings and the muscle 

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

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

 stimulates the receptor 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 influenced by the nerve system. Thus Dreyer found that the blood 

 of the adrenal vein after stimulation of the splanchnics was capable 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, has no such effect. After ligation of the veins or the removal 

 of the adrenals there is 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 receptor substance at the myo- 

 neural junction and thus cooperates with the sympathetic system, i.e., 

 the vaso-constrictor and the viscero-inhibitor and other nerves, to main- 

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

 contraction of the arteriole muscles 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 



