86 Influence of Inanition on Metabolism. 



obtain in the alimentary tract as well as in the tissues. But on the other hand, 

 in the experiments in which food is ingested after fasting, it is certainly true 

 that during the transitional period, there is unlike absorption from the ali- 

 mentary tract, and probably not until two or more days have passed will the 

 conditions be comparable to those of the ordinary metabolism experiment. 



A further factor enters into computations of this nature in that it has 

 commonly been assumed that the chemical elements and compounds in the 

 feces result entirely from unabsorbed food. This is equivalent to saying that 

 the feces are not a true excretory product, but simply residues of undigested 

 food. More recent research is showing that, with certain diets at least, this is 

 far from being the case and that the compounds in the feces are the result of 

 metabolic changes just as surely as are the compounds in the urine. 23 



Until more satisfactory methods for distinguishing between the undigested 

 residues of food in the feces and the products of metabolic changes have been 

 developed, no other alternative presents itself in these computations than to 

 assume that the materials in the feces are undigested food. According to this 

 assumption the actual amount of material absorbed from the food by the 

 body is the difference between the actual weight of the chemical compounds and 

 elements in the food and the weight of the corresponding elements and 

 compounds in the feces. 



It is commonly accepted that all the compounds in the urine result from 

 metabolic activity and yet it is to be borne in mind that preformed extractives, 

 such as creatinine, may be excreted in this manner without undergoing a 

 change. 



As a result of the analyses of urine and respiratory products, as well as 

 the determinations of heat, it is possible to determine the actual katabolism 

 in the body, irrespective of the ingestion of food. Having determined to what 

 extent katabolism has taken place, it is then proper to compare the ingredients 

 of the absorbed food with the corresponding materials katabolized and see 

 in how far the food has sufficed to replace the material broken down. This 

 comparison will also serve to show whether there has been an excess of food 

 and consequent storage of material. In discussing the food experiments made 

 in connection with the study of the influence of inanition on metabolism, the 

 plan will therefore be adopted of first calculating the amount of material 

 katabolized and then determining to what extent the food supplied the necessary 

 material for katabolism. 



In deciding upon a method for recording results of experiments with food, 

 the fact was taken into consideration that the actual katabolism was the most 

 important phase studied. By means of the analyses of urine and the respiratory 



22 For a further discussion of this phase of computing metabolism experiments, 

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



