446 THE METABOLIC PROCESSES OF THE BODY. 



sufficiently soon after death, and in which owing to the suddenness of death 

 there was- no opportunity for stored-up glycogen to disappear, a very large 

 quantity of glycogen has been found in the liver or some other organs. 

 Hence the phenomena of diabetes may be taken as showing, in a much more 

 striking manner than do any experiments, that proteid material taken as 

 food may give rise to hepatic glycogen. 



382. We may now turn to another question, the answer of which is in 

 a measure dependent on the one which we have just discussed. What is the 

 use and purpose of this hepatic glycogen ? What ultimately becomes of the 

 glycogen thus for a while stored up in the liver? 



One view which has been put forward is as follows : We have evidence, 

 as we shall presently learn, that a great deal of the fat of the body is not 

 taken as such in the food, but is constructed anew in the body out of other 

 substances. Both carbohydrates and proteids, taken in excess or under 

 certain circumstances, lead to an accumulation of fat; and we have reason 

 to believe that carbohydrates, on the one hand, and the carbon-holding por- 

 tions of various proteids, on the other, may by some process or other be con- 

 verted into fat. And it has been suggested that the glycogen in the liver is 

 a phase of a constructive fatty metabolism, that it is material on its way to 

 become fat. 



Another view, one which has already been suggested while we were dealing 

 with the manner of formation of glycogen, makes use of the formation of fat 

 for the purposes 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 carbohydrate material, being accumulated when- 

 ever 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. 

 It was formally believed that this sugar underwent an immediate and direct 

 oxidation as it was circulating in the blood, but we have already dwelt 

 ( 360) 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 average com- 

 position is necessary for that great internal medium the blood, in order that 

 the several tissues may thrive upon it to the best advantage, one element of 

 that composition being a certain percentage of sugar. It would appear that 

 some at least if not all of the tissues are continually drawing upon the blood 

 for sugar, and that hence a certain supply must be kept up to meet this 

 demand. On the other hand an excess of sugar in the blood itself would 

 be injurious to the tissues. Arid as a matter of fact we find that the quan- 

 tity of sugar in the blood is small but constant ; it remains about the same 

 when food is being taken as in the intervals between meals. If sugar be 

 injected into the jugular vein in too large quantities or to rapidly, a certain 

 quantity appears in the urine, indicating an effort of the system to throw off 

 the excess and so bring back the blood to its average condition. The main- 

 tenance of such a constant percentage of sugar would obviously be pro- 

 vided for, or at least largely assisted by the liver acting as a structure where 

 the sugar might at once and without much labor be packed away in the 

 form of the less soluble glycogen, at those times when, as during an amyla- 

 ceous meal, sugar is rapidly passing into the blood, and there is danger of 



