CHEMISTRY OF DIGESTION AND NUTRITION. 361 



diet deficient in non-proteid material; that if the supply of this material had 

 been sufficient, none of the additional proteid would have been oxidized. It 

 must be admitted, however, that the experiments of A.rgutinsky compel us to 

 state the proposition above as to the relation between muscular work and 

 proteid metabolism in a more careful way. It is necessary to modify the 

 statement generally made to the extent of saying that muscular work causes 

 no increase in proteid metabolism, provided the supply of non-nitrogenous 

 food is abundant. 



If now we compare the amounts of C0 2 eliminated during work and during 

 rest, it will be found that there is a very decided increase during work. In the 

 experiments made by Pettenkofer and Voit the 0O 2 given off by a man 

 during a day of muscular work was nearly double that eliminated during a 

 resting-day. Indeed, the same fact has been observed repeatedly upon isolated 

 muscles made to contract by artificial stimuli. Assuming, then, that muscular 

 work causes no increase in the nitrogen excreted, but a marked increase in the 

 C0 2 eliminated, we are justified iu saying that the energy of muscular work 

 under normal conditions comes mainly, if not exclusively, from the oxidation 

 of non-proteid material. The machine that does the work, the muscle, is 

 par excellence a proteid tissue, but the normal resting metabolism of its pro- 

 teid substance is not increased by the chemical changes of contraction. Or, 

 to put it in another way, the chemical changes that give rise to the energy lib- 

 erated in contraction may involve only the non-proteid material. It is inter* >t- 

 ing to remember in this connection that the consumption of glycogen, or of 

 the sugar derived from it, is intimately connected with muscular work. The 

 glycogen of the body in an animal deprived of food disappears much more 

 rapidly if the animal is made to work his muscles than if he remains at 

 rest. In an experiment by Kiilz upon well-fed dogs it was found that the 

 glycogen was practically all used up in a single fasting-day during which the 

 animals did a great deal of work. Morat and Dufourt have shown also that 

 a muscle after prolonged contraction takes much more sugar from the blood than 

 it did previous to the contraction, and Harley 1 finds that power to perform 

 muscular work may be increased and susceptibility to fatigue be diminished 

 by eating sugar in quantities. It is, in fact, generally agreed that glycogen i- 

 used up in muscle-contractions, but the way in which the destruction of the 

 glycogen is effected is not definitely known. After the glycogen has been con- 

 sumed it is probable that the other constituents of the body, the fats and the 

 proteids, are called upon to furnish the necessary energy. I'd- this reason 

 we should expect, in a person performing excessive muscular work, that there 

 would be an increased destruction of proteid when the supply of aon-proteid 

 food is insufficient. 



Metabolism during Sleep. — It has been shown that during sleep there is no 



marked diminution of the nitrogen excreted, and therefore no distincl decrease 



in the proteid metabolism; on the contrary, the < '< > 2 eliminated and the 



oxygen absorbed are unquestionably diminished. This latter fact finds its 



1 Journal ,,/ Physiology, 1894, vol. xvi. j>. '.'7. 



