CHAPTER XLVI. 



SECRETION OF THE DUCTLESS GLANDS-INTERNAL 

 SECRETION. 



The term "internal secretion" is used to designate those secre- 

 tions of glandular tissues which, instead of being carried oft" to the 

 exterior by a duct, are ehminated in the blood or lymph. The idea 

 that secretory products may be given off in this way has long been 

 held in reference to the ductless glands, such as the thyroid, pitui- 

 tary body, etc., the absence of a duct suggesting naturally such a. 

 possibility. The term, however, seems to have been employed 

 first by Claude Bernard, who emphasized the distinction between 

 the ordinary secretions, or external secretions, and this group of 

 internal secretions. Modern interest in the latter is due largely to 

 work done by Brown-Sequard (1889) upon testicular extracts, work 

 which itself was of doubtful value. This author was led to amplify 

 the conception of an internal secretion by the assumption that all 

 tissues give off a something to the blood which is characteristic, 

 and is of importance in general nutrition. This idea led in turn to 

 a revival of some old notions regarding the treatment of diseases 

 of the different organs by extracts of the corresponding tissue, 

 a therapeutical method usually designated as opotherapy. Brown- 

 Sequard's extension of the idea of internal secretion has not been 

 justified b}^ subsequent work, and to-day we must limit the term 

 to tissues that have a glandular structure. Experience has shown, 

 that not only the ductless glands, but some at least of the typical 

 glands provided with ducts may give rise to internal secretions, 

 the pancreas, for example. The work done since 1889 has demon- 

 strated fully that some, perhaps all, of the the ductless glands play 

 a role of the very greatest importance in general nutrition. They 

 yield internal secretions of one kind or another, and modern inves- 

 tigations have demonstrated that there is a comphcated interrela- 

 tion among the secretions as regards their action on body metabo- 

 lism. In view of these facts, the entire group of ductless glands or of 

 glands furnishing definite internal secretions is sometimes united 

 under the designation of the endocrin system (endon, within, krino, 

 I separate). The conception that certain glandular organs may 

 give rise to chemical products which on entering the circulation 

 influence the activity of one or more other organs has found 



