CHAPTER IV. 



THE STANDARD METABOLISM OF THE ORGANISM. DEFINITION AND 



DETERMINATION. 



THE complex problem concerning the catabolic processes taking place 

 in the animal organism has been attacked on three different lines, one 

 might almost say by three independent armies of investigators. One 

 line of attack is the study of the respiratory exchange of the animal 

 organism as a whole, its variations from internal causes, and the factors 

 by which it may be influenced. Another line is the study of the ex- 

 change of single organs, tissues, and cells with the variations observed 

 during activity, under the influence of chemical substances and so forth. 

 A third line again is the study of the catabolism of single sub- 

 stances, of the intermediate stages in the processes, of the enzymes and 

 other agencies which bring about catabolism. Though there can be 

 no doubt that ultimately the three attacking forces will have to join 

 hands, to support each other, and to utilize in common the progress 

 achieved by each, we find that at present they are too far apart for 

 concerted action and the achievements in one field do not materially 

 help the advance in the others. 



At present it is legitimate therefore to review them separately, and 

 in this monograph only casual references will be found to the meta- 

 bolism of single organs or cells and none whatever to the catabolism 

 of definite substances. 



In studying the respiratory exchange of an animal we have to do 

 with a quantity which is variable in the extreme. In man the maxi- 

 mum respiratory activity is 10 to 20 times the minimum in one and 

 the same adult individual, and in many lower animals the maximum 

 may be several hundred times the minimum. The problem before us 

 is to define the conditions of these variations, to eliminate them as far 

 as possible, and then to study their influence one by one and quantita- 

 tively. 



The factor which is of paramount importance in determining the 

 metabolism is the functional activity. In the organism as a whole 

 we cannot have metabolism without some functional activity. In in- 



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