XVIII 



CHEMICAL REGULATORS 



Preview. Chemical co-ordination • Regulators of digestive processes • 

 Regulators of general metabolism : Adrenals, thyroid, parathyroids, pan- 

 creas ■ Growth regulators : Thyroid ; gonads and pituitary ; pineal • Repro- 

 ductive organs as regulators • The master gland or "generalissimo," the 

 pituitary : the anterior lobe, growth stimulation, gonad stimulation, lacta- 

 tion hormone, thyreotropic hormone, adrenotropic hormone, blood sugar 

 raising principle, fat metabolism-regulating principle, parathyreotropic 

 principle ; the intermediate lobe ; the posterior lobe • Suggested readings. 



PREVIEW 



Co-ordinating devices are necessary as soon as cells become grouped 

 together in large enough masses to isolate the inner ones from external 

 stimuli. As the cell mass increases in size, there is a tendency for 

 greater division of labor to be developed, and we find organisms evolv- 

 ing with special tissues to perform specific functions. These tissues in 

 turn are woven into more complex systems that call for a still greater 

 division of labor. 



Probably the chief co-ordinating mechanism which keeps the 

 organism in touch with its external environment is the nervous 

 system. Even the primitive nerve net of the coelenterates serves 

 quite adequately in this capacity, while the linear type of nervous 

 system with its more highly specialized co-ordinating centers fur- 

 nishes a more complex and efficient mechanism in the higher forms. 

 There is another equally important, though far less thoroughly under- 

 stood mechanism that acts as an "internal co-ordinator," since both 

 nervous and chemical correlation is necessary to secure a symmetrical 

 development and orderly functioning of the related parts. 



The study of chemical co-ordination is a field literally bristling 

 with thousands of unanswered questions and holding promise of 

 becoming one of the most productive phases of modern physiological 

 and medical research. Within its pages are already told some of 

 the most thrilling tales of intellectual adventure one could hope to 

 encounter. Only a few of these will be enumerated, but we might 

 well seek an answer to such questions as : What are the controlling 

 devices of the body for producing and regulating normal growth? 



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