CHAPTER VII 

 THE FASTING KATABOLISM 



333. Significance. It is a familiar fact that in the absence 

 of feed the life of the animal can be supported for a time at the 

 expense of the materials of the body itself. If sufficient water 

 and oxygen be supplied, those metabolic processes by which 

 energy is liberated for the physiological activities of the body 

 (201, 207) may continue for a considerable period, although, of 

 course, they are ultimately halted by lack of material or im- 

 pairment of the integrity of the protoplasm. The fasting 

 animal in a state of rest, therefore, affords an opportunity to 

 study the demands of the fundamental vital processes un- 

 complicated by the functions of digestion and resorption or by 

 the requirements of growth, fattening or reproduction. 



A qualitative and quantitative knowledge of the expenditure 

 of matter and of energy by the fasting animal, then, is obviously 

 an important step towards ascertaining the supply of feed 

 necessary for various purposes. 



334. Substances katabolized. All the principal compo- 

 nents of the body may be katabolized and yield energy for the 

 support of the fasting organism. 



Fat. It is a familiar conception that fat formation is the 

 body's method of disposing of surplus feed, and that the body 

 fat is a store of reserve fuel material. The converse of this 

 fact is equally familiar. The fasting or insufficiently fed ani- 

 mal loses fat, and may reach a stage of extreme emaciation be- 

 fore the active tissues fail to perform their functions. Obviously, 

 the fasting animal lives largely upon its reserve of fat. These 

 conclusions from common observation have been fully con- 

 firmed by comparative analysis of the carcasses of well-fed and 

 of fasted animals as well as by the results of balance experiments 

 in which the exact nature of the outgo from the body has been 

 determined. 



Carbohydrates. In addition to fat the body contains more 

 or less non-nitrogenous matter in the form of glycogen in the 



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