THE METABOLISM OF FATS AND CARBOHYDRATES 143 



voraciously of starchy food and gaining steadily in fat, 

 breathes out more carbon dioxid than can be accounted 

 for by the oxygen consumed. The excess is a by-product 

 of the process in which sugar with its high percentage of 

 oxygen is made over into fat with a much lower per- 

 centage. 1 



Recourse may be had once more to analogy. Bernard 

 compared the liver to a bank, but we may extend the com- 

 parison to the whole body. The products of digestion are 

 the daily deposits; the oxidations stand for the daily 

 payments. The bank will have a convenient cash balance 

 on hand from which to meet current demands. This is 

 the function of glycogen. The. cash in the bank will 

 be but a small fraction of its total resources, and its varia- 

 tions from hour to hour will signify but little as regards the 

 stability of the institution. So the glycogen of the body 

 is a small reserve and may vary by 50 per cent, within 

 twenty-four hours. The body-fat, like the securities held 

 by the bank, is a large accumulation and less subject to 

 change. If for some time the deposits are in excess of the 

 withdrawals, the officials of the bank will, of course, make 

 new investments. The parallel is clear : the body receiving 

 more carbohydrate than it is expending will not allow it to 

 go on increasing in the liver and muscles, but will begin to 

 convert it to fat. Unhappily, the correspondence fails 

 at one point: a bank which is subject to a "run" may sell 

 its bonds and other holdings that it may have cash to 

 pay its depositors. The obvious suggestion is that the 

 fat of the body will be reconverted to sugar when there are 

 demands to be met and no incoming food. This is not 

 known to occur ; the oxidation of fat during starvation ap- 

 pears to proceed without any such previous change. 



Using another metaphor, though still a financial one, it 



1 Without assuming that the process is fully understood, French 

 authorities have suggested that the principles involved may be shown 

 in the following equation: 



13(C 6 H 12 6 ) = C 55 H 104 6 -f 23(C0 2 ) + 26(H 2 O). 

 (Shafer, " Text-book of Physiology," vol. i, p. 933.) 



