CHAPTER XI 

 INTERNAL SECRETION } 



IT is long since Caspar Friedrich Wolff expressed the idea that 

 ' each single part of the body, in respect of its nutrition, stands to 

 the whole body in the relation of an excreting organ,' and thus 

 emphasized the importance of substances produced by the activity 

 of one kind of cell for the normal metabolism of another. But it is 

 only in recent years that it has become possible to illustrate this 

 mutual relation by any large number of experimental facts. 



Jtertain of the substances taken in from the blood by the liver 

 find their way, after undergoing various changes, into the biliary 

 capillaries, and are excreted as bile; certain other substances, such 

 as sugar and the precursors of urea, are taken up by the hepatic 

 cells, transformed and sometimes stored for a time within them, 

 and then given out again to the bloooi fBile we may call the external 

 secretion of the liverj/glycogen and Area constituents of its internal 

 secretion^] In one sense it is evident that all tissues, whether glands 

 in the morphological sense or not, may be considered as manufac- 

 turing an internal secretion. For everything that an organ absorbs r 

 from the blood and lymph it gives out to them again in some form 

 or other except in so far as it forms or separates a secretion that 

 passes away by special ducts. But it is usual to employ the term 

 only in relation to organs of glandular build, whether provided with 

 ducts or not. For convenience the action of extracts of some other 

 tissues, such as nervous tissue, will also be considered here, although 

 there is no reason to suppose that they form any specific internal 

 secretion. 



The capacity of manufacturing internal secretions of high im- 

 portance can neither be attributed to all glands with ducts nor 

 denied to all other organs. /For the salivary, mammary, and gastric 

 glands may be completely removed without causing any serious 

 effects, while death follows excision of the, so far as mere bulk is 

 concerned, apparently insignificant masses of tissue in the ductless 

 thyroid, parathyroid, suprarenal or pituitary bodies. J 



lt is known that in the case of the liver the internal secretion is 

 more important than the external, for an animal cannot survive 



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