420 GLYCOGEN. [BOOK n. 



examined before any post-mortem changes have had time to de- 

 velope themselves, is absolutely free from sugar. 



Normal hepatic blood was obtained by Pavy, by means of an in- 

 genious catheterisation. He introduced through the jugular vein, into 

 the superior, and so into the inferior vena cava, a long catheter, con- 

 structed in such a manner that he could at pleasure plug up the vena 

 cava below the embouchement of the hepatic veins, and draw blood ex- 

 clusively from the latter ; or vice versa. 



Now the quantitative determination of sugar in blood by any 

 of the methods as yet suggested is open to many sources of error. 

 And when the quantity of blood which is continually flowing 

 through the liver is taken under consideration, it is obvious that 

 an amount of sugar, which in the specimen of blood taken for 

 examination fell within the limits of errors of observation, might 

 when multiplied by the whole quantity of blood, and by the 

 number of times the blood passed through the liver in a certain 

 time, reach dimensions quite sufficient to account for the conversion 

 into sugar of the whole of the glycogen present in the liver at any 

 given time. Hence we may safely conclude that the comparative 

 analysis of hepatic and portal blood, if they do not of themselves 

 prove that the liver is either continually or at intervals converting 

 some of its glycogen into sugar and discharging this sugar into the 

 general system, are at least not sufficiently trustworthy to disprove 

 the possibility of such a discharge of sugar being one of the normal 

 functions of the liver. 



We may therefore regard the view that glycogen is simply a 

 stage in the formation of fat as not proved ; and indeed we shall 

 presently see reason to believe that fat is formed elsewhere. 



Another view makes use of the formation of fat for the pur- 

 poses of analogy only. Seeing that adipose tissue serves as a 

 storehouse of fat which is not wanted by the body at the moment 

 but may be wanted presently, the question readily presents itself, 

 May not the hepatic glycogen have an analogous function ? May we 

 not regard the presence of glycogen in the liver as in large measure 

 due to the fact that it is deposited there simply as a store of carbohy- 

 drate material, being accumulated whenever amylaceous material is 

 abundant in the alimentary canal, and being converted into sugar 

 and so drawn upon by the body at large to meet the general 

 demands for carbohydrate material during the intervals when food 

 is not being taken ? And we can accept this view without being 

 able to say definitely what becomes of the sugar thus thrown into 

 the hepatic blood. Bernard believed that this sugar underwent an 

 immediate and direct oxidation, but we have already dwelt (p. 351) 

 on the objections to such a view. It is sufficient for us at the 

 present to admit that the sugar is made use of in some way or 

 other. 



Now, many considerations lead us to believe that a certain 



