CHAP, v.] NUTRITION. 863 



material still remaining in the muscular fibres and not to its 

 supplying new raw material. 



Dextrose is, as we have repeatedly said, always present in the 

 blood in small quantity, and appears to be the only carbohydrate 

 constituent of blood-plasrna. Experiments carried out on a large 

 animal, such as the horse or cow, have shewn that the venous blood 

 coining from a muscle contains less dextrose than the arterial 

 blood going to the muscle, and that the difference is much 

 increased by throwing the muscle into contraction. From this we 

 may provisionally conclude that dextrose is an essential part of 

 the food of the muscle. And this view seems to be supported 

 by the following experiment. In ourselves by recording the move- 

 ments of a part of the body we may measure the work done by 

 a muscle or group of muscles ; by recording the amount of the 

 repeated bending of a finger for instance we may measure the 

 work done, under varying conditions, by the flexor muscle for the 

 finger. Now it is found by this method that the power of a 

 muscle is greatly and rapidly increased, and the effects of fatigue 

 markedly postponed, by swallowing a small quantity of sugar. Of 

 course, it does not necessarily follow that the beneficial effect, 

 which is very marked and constant, is simply due to the sugar 

 being absorbed, carried as dextrose to the muscle, and utilized 

 by the muscular tissue ; the effect may be produced in some other, 

 possibly roundabout, way; but, until the opposite is shewn, the 

 experiment may be taken as supporting the view laid down above. 



The blood as we have seen also contains a certain amount 

 of fat; and if we push the analogy between the whole body 

 and the muscle we may infer that the muscle takes up fat as food 

 for itself from the blood. But we have no experimental evidence 

 in favour of this. Moreover we have seen that fat and carbo- 

 hydrate are in the animal body more or less transferable. We 

 have distinct proof that the body can transform carbohydrate into 

 fat ; and it is very probable that it can transform fat into 

 carbohydrate. Seeing how much more easily a soluble diffusible 

 carbohydrate like sugar can be carried from place to place by the 

 fluids of the body than can immiscible fats, it seems reasonable to 

 suppose that when the body has to draw upon its store of fat 

 in the cells of adipose tissue, the fat on leaving the fat-cell is 

 transformed into sugar, its carbon so to speak being dealt out to 

 the tissues in the form of dextrose. Indeed we may perhaps, 

 dwelling on the fact that a muscle though itself essentially 

 of proteid build, turns over ( 87) in its daily work so much more 

 carbon than nitrogen, entertain the view that what muscle wants 

 as food is a certain amount of proteid plus an additional quantity 

 of carbon in some form or other, and that dextrose is a convenient 

 form in which the additional carbon can be supplied. And we 

 may hold this view without prejudice to any opinion that the 

 carbon so brought, while being built up into the living substance, 



