METABOLISM 



The term metabolism may, therefore, be applied to the chemic changes 

 which materials undergo, under the influence of living cells. It comprises 

 (i) the elaboration on the part of the living material, of substances of rel- 

 atively low composition into substances of higher and more complex com- 

 position anabolism; and (2) their subsequent reduction to substances of 

 lower and. less complex composition, including as well, the reducton of the 

 relatively less complex food materials to simple compounds katabolism. 



For many reasons it is desirable to know, as far as this is possible the 

 extent and character of the tissue changes, as well as the successive chemic 

 changes which the food materials undergo in their transit through the 

 body from day to day. 



In order to obtain this information it is necessary to place the subject of 

 the experiment under conditions which permit of the collection of the ex- 

 cretions for purposes of analysis, and then to deduce from the nitrogen and 

 carbon they contain, the amounts of the tissue materials metabolized in the 

 absence of food; or the amounts of the food materials metabolized when the 

 ordinary amounts of food are consumed. Supplementary facts from the 

 field of physiologic chemistry throw much light on many of the intermediate 

 chemic stages. 



The methods by which a metabolism experiment is conducted have been 

 detailed on pages 118-120. 



In various sections of the preceding pages some of the facts pertaining 

 to the metabolism of the body have been presented and considered, and 

 it will suffice in this connection to summarize some of the facts already 

 alluded to and to add others not heretofore mentioned. 



Before considering the metabolism of the individual organic food ma- 

 terials as it unfolds itself in the animal body under physiologic conditions, 

 it is of advantage to consider the metabolism of living material as it mani- 

 fests itself when the animal or the human being is deprived of food for a 

 variable length of time or during the starvation process. 



THE METABOLISM OF LIVING MATERIAL DURING STARVATION 



When an animal is subjected to the conditions of a metabolism experi- 

 ment and deprived of all food except water and oxygen, it is a relatively simple 

 matter to collect the excretions, to analyze them for nitrogen and carbon and 

 then to calculate from the amounts of each the amounts of protein and fat 

 metabolized from day to day. The carbohydrates may be left out of con- 

 sideration in a prolonged experiment. The following experiment is 

 illustrative. The man fasted five days and performed light work in the 

 respiration chamber. 



METABOLISM OF J. A. IN STARVATION 



