952 THE INTERNAL SECRETIONS 



data pertaining to the effects following the removal of the thyroid 

 bodies which were based in the main on the clinical observations of 

 J. L. and A. Reverdin and Kocher on post-operative myxedema. 

 Somewhat later Glover, Schafer (1895), Cybulski (1895), Biedl (1898) 

 and Dreyer (1899) studied the action of suprarenal extract upon the 

 cardio- vascular system. In all these instances, it was shown that our 

 body contains certain aggregates of cells which possess an altruistic 

 function, because they supply the organism as a whole with substances 

 having to do with its general welfare. The medium through which 

 these organs are able to exert this influence, is the blood or more par- 

 ticularly the blood plasma. 



Classification of the Internal Secretions. — In 1902, Bayliss and 

 Starling showed that a flow of pancreatic juice may be evoked b}^ 

 means of some agent derived from the mucous membrane of the duo- 

 denum. To this substance these investigators applied the name of 

 secretin. At about the same time Starling and Claypon demonstrated 

 the existence of a similar stimulant in the female generative organs 

 which induces a growth of the mammary glands. Starling, therefore, 

 proposed to apply to all these chemical agents or messengers the name 

 of ''hormone, " from the Greek opy^doi, to stir up or excite. But in- 

 asmuch as some of these cellular products may also retard a function, 

 Schafer^ advises to include all of them under the general term of auta- 

 coid substances, from the Greek olkos, a remedy and auros, natural. 

 Thus, an autacoid represents any drug-like principle which is produced 

 in the internal secreting tissues and organs. In accordance with their 

 action, these substances may then be grouped as hormones or chalones 

 (Greek x«Xaco, to make slack). The former are excitatory and the 

 latter inhibitory in their nature. 



In most instances these internal agents are as yet wholly unknown 

 to us chemically, and their presence can only be detected in an experi- 

 mental way. In some cases, however, they have been isolated, and 

 have been dealt with as definite chemical entities. Carbon dioxid is a 

 substance of this kind, because it plays the part of a hormone in stimu- 

 lating the respiratory center whenever produced in excess. Another 

 one is adrenalin, a crystalline body obtained from the adrenal glands by 

 Takamine.2 It constricts the blood-vessels and raises the blood pres- 

 sure. As a third might be mentioned hydrochloric acid, because it 

 liberates secretin and as a fourth, idiothyrin which exerts a peculiar 

 action upon the neuro-muscular mechanism. By far the greatest 

 number of these autacoids, however, are of unknown composition and 

 their presence can only be proved physiologically, for example, by in- 

 jecting the extracts of the tissues in which they are supposed to exist 

 into the blood-stream. 



Starling emphasizes the fact that hormones belong to the crystal- 

 loids rather than to the colloids. Consequently, they are relatively 



^ Intern. Congress of Med., 1913. 

 2 Therap. Gazette, xvi, 1901, 221. 



