INTERMEDIATE METABOLISM OF CARBOHYDRATES 393 



was determined. Fifty-two grams of glycogen were obtained, corre- 

 sponding to 1.16 grams of glycogen per kilogram of body-weight. 

 A normal well-fed dog of similar dimensions contained 3.8 grams of 

 glycogen per kilogram of body-weight. Even after four weeks of 

 starvation a similar dog was found to contain 1.5 grams of glycogen 

 per kilogram of its body-weight, so that somewhat less than ten hours 

 of severe muscular exertion reduced the glycogen reserves of the body 

 to a greater extent than four weeks of sheer starvation. 



So far, then, we have proved that muscular energy may be and is 

 derived, in part at least, from the consumption of carbohydrate mate- 

 rials. The question now remains, what proportion of the energy of muscu- 

 lar work is provided by the carbohydrates of the food? For while the 

 experiments which we have cited show that a part, and probably a 

 large part of the energy expended in muscular work is certainly derived 

 from carbohydrates, they do not preclude the possibility that an 

 important proportion of the necessary heat-units may be supplied by 

 other foodstuffs, for example by Proteins. 



This question was answered as early as 1865 by a classical experiment 

 which was performed by Fick and Wislicenus. These observers 

 ascended Mount Faulhorn, climbing to a height of 1956 meters above 

 the starting-point. For seventeen hours before they started, during 

 the six hours occupied in the ascent, and for six hours following the 

 completion of the ascent they consumed no food which contained 

 nitrogen. The urine passed during the ascent and in the six hours 

 succeeding the ascent was collected and from its nitrogen-content the 

 total quantity of body-protein which had been decomposed was 

 estimated. It was found that Fick had decomposed 38.3 grams of 

 protein while Wislicenus had decomposed 37.0 grams. Now if we 

 assume, which, of course is not the fact, that all of the protein was 

 decomposed so completely as to produce the end-products of perfect 

 combustion, namely CO 2 , H 2 O and nitrogen, this quantity of protein 

 would have liberated 250 calories, equivalent, if it were wholly con- 

 verted into mechanical work, to 106,000 kilogram-meters. But Wisli- 

 cenus, for example, weighed 76 kilograms, and the work which he 

 actually performed in the mere effort of raising his body through 

 1956 metres was 76X1956=148,656 kilogram-meters, so that upon 

 the most excessively liberal computation the protein which was decom- 

 posed during and after the ascent could not possibly have furnished 

 the energy consumed in the ascent. As a matter of fact, the actual 

 yield of calories when protein is burnt in the body is much less than 

 that which would be derived if combustion were complete, for instead 

 of nitrogen being formed the oxidation stops with the production of 

 Urea which has a very considerable heat-value of its own and which 

 is voided from the body and not utilized. Furthermore no machine is 

 known, not even a living machine, which can quantitatively convert 

 heat into mechanical work. In fact actual measurements have shown 

 that only twenty per cent, of the heat-value of foods is, as a rule, 



