THE DUCTLESS GLANDS. 



BY SWALE VINCENT, M.D., D.Sc, 

 Professor of Physiology in the University of Manitoba, Winnipeg. 



Introduction. 



The idea of " secretion " has from the earliest period of physio- 

 logy been associated with a " gland." The essential of a gland 

 is a surface, more or less involuted, provided with " epithelial " 

 cells, usually of a columnar or cubical shape, and characterised 

 by the presence of granules of the substance to be secreted or 

 its precursor. In a typical gland such as the submaxillary the 

 primitive plan of an extended surface or a tubular depression 

 has been so far superseded that the organ consists of a compact 

 conglomeration of secreting cavities leading into " ducts " which 

 become successively larger and larger till the chief " duct " of 

 the gland is reached. 



But some structures which resemble glands in their general 

 characters and even in the nature of their cellular elements are 

 found to possess no " alveoli " or secreting cavities and no ducts. 

 Hence they have been called " ductless glands," or in Germany 

 more usually " Blutgefassdriisen." The assumption was at once 

 made that since these structures had the characters of glands 

 they must " secrete." But since there was no communication 

 with a free surface the hypothesis arose that in these cases the 

 specific secretion is passed into the blood stream, and the process 

 is termed " internal secretion." In some cases the material 

 secreted by the ductless glands is passed not directly into the 

 blood stream, but indirectly by way of the lymphatics. This 

 is usually supposed to apply to the specific secretion of the 

 thyroid gland. 



The terms "ductless gland" or " Blutgefassdruse " were 

 originally applied to a very varied group of structures, in- 

 cluding the thyroids and parathyroids, the suprarenal capsules, 

 the thymus gland, the pituitary body, the spleen, and the 

 lymphatic glands. But some of these, viz. the spleen and 

 lymphatic glands, have not a "glandular" structure, that is, 



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