8o INTERNAL SECRETIONS 



other organs or on the metaboHsm in general by the inter- 

 mediation of the body fluids is often taken as the only character- 

 istic feature of what we call an internal secretion par excellence. 

 But I think that such a conception, which seems now to be 

 very widespread, cannot be of much use in physiology. If 

 any kind of specific action by intermediation of a katabolic 

 substance entering into the body fluids is alone sufficient for 

 designating this substance an internal secretion, there is 

 in the multicellular organisms of animals and plants, no 

 organ or no cell which could not be designated an organ of 

 internal secretion. If one takes this standpoint, it is possible 

 to speak of an internal secretion of the lungs, of the skin, or any 

 other organ. But an organ of internal secretion should not be 

 simply characterised by the fact that it is connected with other 

 organs by the intermediation of chemical messengers or hor- 

 mones (Bayliss and Starling, 1906). It must also be an organ 

 which has no other function than to secrete chemical messengers 

 or hormones of a special chemical composition and such as are 

 never produced in other organs. Organs such as the thyroid 

 gland, the hypophysis, the adrenals, and so on, are only 

 characterized functionally by these specific substances which 

 have a specific action. So I think that it would be best to 

 restrict the term '* endocrine organ " in the first instance to glands 

 which, as far as we know, have no other function than the 

 secretion of specific substances which enter into the blood 

 and influence the other organs in a specific manner, i.e., organs 

 secreting chemically specific hormones. 



Such a definition of an endocrine organ is not an ideal one. 

 But, unfortunately, as so often happens in physiology, we 

 cannot hope for an ideal definition on account of the numerous 

 transitional conditions which exist. There are organs pro- 

 ducing chemically specific hormones, i.e., performing an 

 endocrine function besides their other well-known functions; 

 this is the case with the pancreas, with the mucosa of the 

 duodenum or small intestine, and with the sexual glands; 

 the same may be true also for other organs, as for the skin. 

 We must never forget that knowledge of the secretion of 

 chemically specific hormones is merely additional biochemical 

 knowledge of the mutual relations between the organs in the 

 body; endocrinology in the larger sense would be only another 

 name for biochemistry. 



