CHAP, v.] NUTRITION. 827 



evidence is all against this view. In fault of actual knowledge we 

 are led to infer that it is in the liver oxidized into carbonic 

 acid and water, thus adding its contribution to the supply of 

 heat, or prepared in some way for oxidation elsewhere. Probably 

 such a change is not confined to the liver, but takes place 

 in other organs such as the spleen. Thus -the kind of action 

 on which we dwelt in treating of urea, namely that the products 

 of the metabolism of one organ are carried to other organs 

 for further elaboration and possible utilization applies to the 

 non-nitrogenous as well as to the nitrogenous products of 

 muscular metabolism ; and if a muscle gives rise to other non- 

 nitrogenous products than carbonic and lactic acid these are 

 probably disposed of in some such way as the lactic acid. In 

 speaking of glycogen in the winter frog ( 460) we said that 

 possibly the glycogen so stored up might arise from sugar 

 brought to the liver from other tissues. If that be so, we should 

 further expect that some at least of that sugar, either as such 

 or as some allied substance, would come from the skeletal muscles 

 which form so large a part of the body of the frog; and if so, 

 we must conclude that under the special circumstances obtaining 

 in the winter frog the muscles discharge into the blood a non- 

 nitrogenous product not in the form either of carbonic or lactic 

 acid. It is perhaps however more probable that the sugar in 

 question comes from a metabolism of the fat stored up in the 

 ' fatty bodies ' and elsewhere. 



545. As far as we can see at present the plan of nutrition 

 thus briefly sketched out for muscle holds good for the other 

 tissues as well, the chief or at least the most conspicuous differ- 

 ences bearing on the nature and properties of and the changes 

 undergone by the material formed by and held by the more 

 distinctly structural framework. Thus the mucin of the salivary 

 mucous cell finds its analogue either in the contractile substance 

 itself, or more probably in some early nitrogenous product of the 

 explosion of the contractile substance, such as may correspond to 

 the myosin of rigid muscle. The metabolism of the hepatic cell 

 seems as we have seen to be especially characterised by its 

 returning to the blood a body, viz. sugar, still containing a 

 considerable amount of energy, available for use in other parts 

 of the body. And this suggests the question whether in the 

 normal metabolism of muscular substance a similar something, 

 still holding a considerable quantity of energy, some proteid 

 substance for instance, may not be returned to the blood ; so 

 that the metabolism of muscle is imperfectly described in saying 

 that the results are carbonic and lactic acids and an antecedent 

 of urea. If this be so, then muscles may be of other use to the 

 body at large than as mere contractile machines, just as the liver 

 has other uses than the production of bile. And the same con- 

 siderations may be applied to the other tissues as well. 



