Katabolism of Glycogen. 463 



necessary to consider the fat katabolism along with the variations in muscular 

 activity in order to obtain an intelligent conception of the causes for the 

 variations in the results for fat. In a subsequent section the relation between 

 the muscular activity and protein, fat, and carbohydrate katabolism, along with 

 a number of other factors of metabolic activity, is considered. 



KATABOLISM OF GLYCOGEN. 



In all respiration experiments thus far made, in which the total income and 

 outgo for 24 hours has been determined, it has been assumed that the store of 

 glycogen in the body remains constant during the experiment, or if there are 

 fluctuations during the day, that the amount in the body at the beginning and 

 end of each experimental day remains unchanged. For experiments with 

 normal diets in which a maintenance ration is supplied, this assumption may 

 not be entirely erroneous. The study of fasting katabolism, on the other hand, 

 involves such abnormal conditions that the assumption that the glycogen con- 

 tent of the body remains constant is hardly justified. With the development 

 of the present form of apparatus in use in the laboratory of Wesleyan Univer- 

 sity, it was possible to obtain direct evidence regarding the absolute amount of 

 oxygen absorbed by man per day. It has recently become possible to compute 

 the loss of body material, not only the amounts of protein and fat, but also the 

 amount of glycogen, and in these experiments the quantities of glycogen 

 katabolized per day, have been computed. All earlier experimenters assumed 

 that the total carbon elimination minus the carbon of the katabolized protein, 

 was derived from the katabolism of fat, but accurate measurements of the oxy- 

 gen intake permit an apportionment between the fat and the glycogen of the 

 carbon eliminated other than carbon of katabolized protein. 



Food was administered in the first series of experiments with which this 

 apportionment was attempted, 101 although in some instances in amounts con- 

 siderably less than that required for maintenance. The first observations 

 regarding the glycogen katabolism of fasting man made with this apparatus 

 are here recorded. The method of computing the amount of glycogen has 

 been elaborated in connection with experiment No. 59, and the possible errors 

 of the method (and they certainly exist) have been pointed out in a discussion 

 elsewhere. 152 



Eecognizing, then, the possibilities of error in this determination, the results 

 are given as representing the closest approximation to the true glycogen 

 katabolism that, so far as we are aware, has yet been made. The respiratory 

 quotient commonly used for determining the apportionment of the combustion 

 between fat and glycogen is not, at least in its ordinary sense, here used. 



151 U. S. Dept. Agr., Office of Expt. Sta. Bui. 175. 



152 Carnegie Institution of Washington Publication No. 42; U. S. Dept. Agr., Office 

 of Expt. Sta. Bui. 175. 



