CHEMICAL REGULATORS :591 



What starts and governs the changes in voice and body that accom- 

 pany the maturing of reproductive systems? Wluit is the explana- 

 tion of that last little ounce of strength which enables a sprinter 

 to put on the final burst of speed? How can such correlation be 

 possible without the existence of a ''master mind" for the l)ody? 

 Answers to these questions will be found in the pages that follow. 



Chemical Co-ordination 



Our knowledge of chemical regulation of the body is far from 

 complete. Workers in the field of endocrinology, as in other fields, 

 are continuously pushing back the frontiers of ignorance, at best a 

 slow process. Nevertheless, each year new excitants, or hormones, 

 are discovered, their effect noted, and their refinement or synthesis 

 accomplished. Rarely there occurs the discovery of the existence of 

 a new and hitherto unsuspected gland that produces one of these 

 hormones. Thus far we know quite definitely that the thyroids, 

 parathyroids, pituitary, gonads, liver, placenta, adrenals, pancreas, 

 the mucosa of the stomach and intestine, and possibly the pineal 

 and thymus glands, function as ductless or endocrine glands. In 

 some instances more evidence is needed, but on the whole a ma- 

 jority of scientists are in agreement regarding this list. 



Early zoologists, including such leaders as Johannes Miiller and 

 Jakob Henle, failed to attach enough significance to the ductless 

 glands. According to Rogers,^ the former stated that "the ductless 

 glands are alike in one particular — they either produce a change in 

 the blood which circulates through them, or the lymph which they 

 elaborate plays a special role in the formation of blood or chyle." 



Probably the first experimental study in endocrinology was made 

 by A. A. Berthold of Gottingen in 1849 when he began a study of 

 the results following the removal of the testes of fowls. Shortly after 

 this Claude Bernard, Addison, and Brown-Sequard made significant 

 contributions. The first of these investigators worked on the liver, 

 while the other two studied the adrenals. Brown-Sequard actually 

 extirpated the adrenal glands and noted that the accomjjanying 

 weakness and death could be prevented by transferring blood from a 

 normal animal to the one from which the adrenals had been removed. 



From the physiological point of view, endocrine glands may be di- 

 vided into five large groups as regulators of : (1) digestion ; (2) general 



' Quoted by permission of the publishers from Rogers, C. G., Textbook of Comparative Phyni- 

 oiogy, p. 361. McGraw-Hill Book Company, 1927. 

 H. W. H. — 26 



