THE ENDOCRINE ORGANS 



AN INTRODUCTION TO THE STUDY 

 OF INTERNAL SECRETION 



CHAPTER I 



GENERAL CONSIDERATIONS 



Internal Secretions and the Organs which Furnish Them 



Material which is passed into the blood or lymph from any tissue or 

 organ of the body forms its internal secretion, and organs which are not 

 known to possess any other function than that of passing such material 

 into the blood or lymph are internally secreting or endocrine organs. 1 

 This term is not usually extended to organs like the lymphatic glands, 

 of which the material production is of a morphological character, although 

 until recently all such organs used to be included along with the true endo- 

 crine glands, the functions of which were at that time unknown, in the 

 general expression of ductless glands. Under this last term were comprised 

 not only the organs to which we now commonly ascribe internally secreting 

 functions, such as the thyroid, parathyroids, the suprarenal capsules or 

 adrenals, the pituitary body or hypophysis cerebri, and the pineal gland 

 or epiphysis cerebri, but also the thymus gland, the tonsils, lymph-glands 

 and lymph-follicles, and the spleen ; with these the bone-marrow is associated. 

 Regarding the thymus gland, although some evidence has been adduced 

 that it may yield an internal secretion to the blood which exercises a 

 specific action upon growth and development, and especially the matura- 

 tion of the generative organs, it appears both developmentally and 

 structurally to resemble the tonsils, which are generally allowed to be 

 structures of a lymphatic nature, and like the tonsils most of its cells 

 are lymphocytic in character. The spleen has been described as furnish- 

 ing an internal secretion which activates the proteolytic ferment of the 

 pancreatic juice ; and the contractions of plain muscular tissue, especially 

 that of the intestines, have been supposed to be stimulated by another 

 substance formed in the organ. But the proof of the existence of such 

 internally secreting functions in connexion with most of these lymphoid 

 structures is so inferior to that which we possess regarding the thyroid, 



1 From o'Soy, within, and icpiVw, to separate. 



1 



