A HISTORY OF SCIENCE 



seems utterly disproportionate to its enormous size, par- 

 ticularly when it is considered that in the case of the 

 human species the liver contains normally about one- 

 fifth of all the blood in the entire body. Bernard dis- 

 covered that the blood undergoes a change of composi- 

 tion in passing through the liver. The liver cells (the 

 peculiar forms of which had been described by Purkinje, 

 Henle, and Dutrochet about 1838) have the power to 

 convert certain of the substances that come to them 

 into a starchlike compound called glycogen, and to 

 store this substance away till it is needed by the organ- 

 ism. This capacity of the liver cells is quite indepen- 

 dent of the bile-making power of the same cells ; hence 

 the discovery of this glycogenic function showed that 

 an organ may have more than one pronounced and 

 important specific function. But its chief importance 

 was in giving a clew to those intermediate processes 

 between digestion and final assimilation that are now 

 known to be of such vital significance in the economy 

 of the organism. 



In the forty odd years that have elapsed since this 

 pioneer observation of Bernard, numerous facts have 

 come to light showing the extreme importance of such 

 intermediate alterations of food-supplies in the blood as 

 that performed by the liver. It has been shown that 

 the pancreas, the spleen, the thyroid gland, the supra- 

 renal capsules are absolutely essential, each in its own 

 way, to the health of the organism, through metabolic 

 changes which they alone seem capable of performing ; 

 and it is suspected that various other tissues, including 

 even the muscles themselves, have somewhat similar 

 metabolic capacities in addition to their recognized 



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