286 THE METABOLISM OF FAT 



temperature. The temperature of the in and out going water is 

 taken, and the volume of circulating water measured. 



By determining the carbon and nitrogen balance between the 

 food fed and the total excreta, any gain or loss of fat and 

 proteid can be calculated. A gain of 66* 67 grm. N equals 100 

 grm. of proteid, and this will contain 52-52-6 grm. of carbon. 

 Any gain of carbon in excess of the amount stored as proteid 

 must be in the form of fat, excepting the very limited amount of 

 glycogen. Every grm. of carbon stored above that put on as 

 proteid will represent 1*3 grm. of fat. Similarly if carbon be lost 

 while the nitrogenous balance is preserved, the loss must come 

 from body fat. The experiments require to be conducted for 

 comparatively long periods, because any small gains or losses of 

 carbon are rendered ambiguous owing to the presence of some 

 300 grm. glycogen in ,the body. 



By the Zuntz method the subject breathes through a meter, 

 and the revolution of the meter causes the continuous collection 

 of a sample of expired air. The total volume breathed is thus 

 obtained, and analysis gives the composition of the expired air, 

 while that of the inspired air can be reckoned if the barometric 

 pressure, temperature, and humidity be known. The 2 use is 

 taken by Zuntz as the better indicator of metabolism, because 

 of the tendency either for the C0 2 or its precursors to 

 accumulate in the muscles during hard work, the excess being 

 given out during the subsequent period of rest. From the 

 respiratory exchange the respiratory quotient is calculated, and 

 this throws light on the character of the material consumed. 

 When the quotient approaches 1-0, as after a mixed meal, energy 

 is chiefly obtained from carbohydrate, and when the quotient 

 nears 07, as before breakfast after a light supper, the body fat 

 is the source of energy. Intermediate values of the quotient give 

 more ambigous results ; but if the amount of 2 consumed and C0 2 

 produced in the oxidation of any one of the three groups of food- 

 stuffs be known, it is a comparatively simple matter to calculate 

 the proportion in which the other two enter into the reaction. 

 Now the total urinary N gives approximately the measure of the 

 proteid katabolism. Knowing the composition of the nitrogenous 

 urinary products, it is possible to compute approximately the 

 amount of C, H, and in these, and then to calculate the amount 

 of oxygen required to oxidise the non-nitrogenous residue of the 



