CHAPTER XI 

 INTERNAL SECRETION ENDOCRINE GLANDS 



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. 



Certain 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 subs.tances, 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 blood. Bile we may call the external 

 secretion of the liver, glycogen and urea 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 

 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. Typical endocrine* glands (that is, glands producing 

 an internal secretion) are the adrenals, thyroid, parathyroid, 

 pituitary, thymus, etc. 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. 

 * From ZvSov, within, and xplvu, I separate. 

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