CHEMICAL CORRELATION OF RESPIRATORY ACTIVITIES 369 



it is chemically related to Adrenaline, for adrenaline, like the Tyrosine 

 from which it is probably derived, is readily converted into highly 

 colored substances by oxidizing-agents and by oxidizing-ferments, 

 especially by the Tyrosinase which occurs in many vegetable tissues, 

 particularly those of fungi, and also in certain animal tissues, as, for 

 example, in tumors arising in the suprarenal bodies (melanomas) and 

 in the ink-sac of the cephalopod sepia. 



The blood-pressure raising substance, adrenaline, which occurs in 

 the medulla, or inner portion of the suprarenal gland, is capable, when 

 administered intravenously, of correcting the excessively low blood- 

 pressure in animals with the suprarenals excised, or in Addison's disease, 

 but it does not avail to prevent the ultimate death of the animals and 

 it is probable that other substances essential to life are produced by 

 these glands besides adrenaline. It is possible that the cortex of the 

 gland, which has an epithelial origin and differs both in structure and 

 embryological development from the medulla, may play an equally 

 essential part in the bodily economy. This is indicated in the first 

 place by the fact that serious symptoms of adrenal insufficiency may 

 accompany degenerative changes affecting the cortex alone, and further- 

 more by the remarkable effect of extensive superficial Burns upon the 

 cortex. Burns or scalds, if at all extensive, are followed by lesions of 

 the suprarenal cortex and especially by minute hemorrhages therein. 

 These changes are progressive for several days following the injury, and 

 are prominent in instances of deferred death resulting from extensive 

 burns or scalds. The unusual abundance of Lipoids and especially of 

 Cholesterol Esters in the suprarenal cortex is suggestive of a function 

 related to the lipoid metabolism, but the nature of this function 

 remains unknown. 



It is of the active physiological principle of the medulla, namely 

 Adrenaline, that our knowledge is most extensive. This substance, 

 when injected intravenously in minute amounts (0.001 mg. and upward 

 in a dog), causes a marked rise in blood-pressure (Fig. 22). This 

 phenomenon is one of many consequences of the general action of 

 adrenaline in stimulating the Myoneural Junctions of the muscles inner- 

 vated by the sympathetic system. The action is not upon the nerves 

 themselves, or upon their anatomically visible endings, for it is more 

 and not less pronounced when the nerve is cut and allowed to degener- 

 ate up to and including its anatomical connection with the muscle. 

 The action is not upon muscle-fibers themselves, for in the first place 

 muscles not innervated from the sympathetic system are not affected 

 by adrenaline, and in the second place the muscles innervated by the 

 sympathetic system are not all affected alike, for if inhibitory fibers 

 predominate the muscle is relaxed, while if stimulatory fibers predomi- 

 nate the muscle is contracted. The glandular tissues are variously 

 affected, for if the adrenaline stimulates their secretory activity, the 

 contraction of the bloodvessels and the consequently diminished blood- 

 supply operate in a contrary direction. In the kidneys the diminished 

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