ON NUTRITION IN GENERAL. 507 



ative value of these substances in maintaining or restoring the irritability 

 of muscle. It is found that when the washed-out frog's heart ( 148) is fed 

 with defibrinated blood, the restoration is as good as with whole blood ; and 

 that while the effects of globulin are uncertain, and while peptone and albu- 

 rnose appear to act in an injurious manner, the restorative effects of serum- 

 albumin are marked. From these results we may provisionally infer that 

 the muscle in its (total) anabolic changes takes up and so lives upon the 

 serum-albumin of the blood. But this conclusion must be regarded as pro- 

 visional only, and indeed uncertain. For we must remember that the blood 

 supplies not only the food (including oxygen) for the muscle, but also the 

 conditions under which the muscle can live and avail itself of the food 

 offered to it. The complex actions through which a certain quantity of 

 proteid and other material is built up into living muscular substance, need 

 for their execution a favorable medium, need certain physical and chemical 

 conditions ; and it may be that the favorable influence of serum-albumin is 

 simply due to its presence in some way assisting the transformation into 

 living substance of raw 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 contituent of blood- 

 plasma. Experiments carried out on a large animal, such as the horse or 

 cow, have shown that the venous blood coming 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. 



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 favor of this. Moreover, we have 

 seen that fat and carbohydrate are, in the animal body, more or less trans- 

 ferable. 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 im- 

 miscible 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 

 ( 85) 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, may be again ar- 

 ranged as fat, and in the course of the metabolism of the muscle may be 

 later on separated from the living substance and deposited in the fibre as 

 globules of fat. But our knowledge is at present insufficient to decide 

 whether this view is true or not. 



The various salts brought to the muscle by the plasma, though they supply 

 no energy, are as essential to the life of muscle as the energy-holding proteid 

 or carbon compound ; and experiments made with regard to some of them, 

 calcic salts, for instance, show that their presence or absence materially affects 

 the maintenance or restoration of irritability. Some of these probably play 



