CH. XLL] 



GENERAL METABOLISM 



613 



The two sides of metabolism may be compared by means of a 

 balance-sheet, and the necessary data for the construction of such a 

 comparison are: 



(1) The weight of the animal before, during, and after the 

 experiment. 



(2) The quantity and composition of its food. 



(3) The amount of oxygen absorbed during respiration. 



(4) The quantity and composition of urine, faeces, sweat, and 

 expired air. 



(5) The amount of work done, and the amount of heat developed. 

 (The subject of animal heat will be considered in the next two chapters.) 



Water is determined by subtracting the amount of water ingested 

 as food from the quantity lost by bowels, urine, lungs, and skin. 

 The difference is a measure of the katabolism of hydrogen. 



Nitrogen. The nitrogen is derived from proteins, and appears 

 chiefly in the urine. Smaller quantities are eliminated in sweat and 

 faeces. From the amount of nitrogen so found, the amount of 

 proteins which have undergone katabolism is calculated. Proteins 

 contain, roughly, 16 per cent, of nitrogen ; so 1 part of nitrogen is 

 equivalent to 6 '3 parts of protein ; or 1 gramme of nitrogen to 30 

 grammes of flesh. 



Fat and Carbohydrate. Subtract the carbon in the katabolised pro- 

 tein (protein contains 54 per cent, of carbon) from the total carbon 

 eliminated by lungs, skin, bowels, and kidneys, and the difference 

 represents fat and carbohydrate which have undergone katabolism. 



Balance of Income and Discharge in Health. 



In Chapter XXX. tables are given of adequate diets; these 

 will in our balance-sheet represent the source of income ; the other 

 side of the balance-sheet, the expenditure, consists of the excretions. 



We may select as our example a typical table of this daily 

 exchange of material on an ordinary diet from the work of Petten- 

 kofer and Voit. In the first experiment the man did no work. 



