866 INFLUENCES DETERMINING NUTRITION. [BOOK n. 



acid, sarcolactic acid. Did any considerable amount of oxidation 

 take place in the blood stream while the blood is flowing along 

 the larger channels, subject only to the influence of the vascular 

 walls, we might fairly expect that the lactic acid discharged from 

 the muscles would be subjected to oxidising influences while still 

 within the blood stream of the larger channels. We have how- 

 ever no satisfactory evidence of any lactic acid being oxidised 

 in this way. On the contrary, there is a certain amount of 

 experimental and other evidence that lactic acid present in the 

 blood is somehow or other disposed of by the liver; and that if 

 the liver fails to do its duty lactic acid may appear in the urine. 

 It is tempting to suppose that it might there by a synthetic effort 

 be converted into glycogen, the liver thus utilizing some of the 

 muscular waste product, but the experimental and other 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. 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 nitro- 

 genous 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 



