174 SCIENCE PROGRESS 



respects is nearer to the views of Liebig than to those which we 

 have described as based upon recent experimental work, renders 

 it necessary to make momentary reference to this controversy 

 before closing. 



According to Voit's teaching the greater part of the proteid 

 which is absorbed from the bowel is too rapidly metabolised for 

 us to believe that it has ever formed part of living structures in 

 the body. (On this point, it will have been seen, recent views 

 are entirely in harmony with those of Voit.) The structural 

 materials are relatively stable, and their breakdown and re- 

 construction are slow processes. The proteid so rapidly dealt 

 with is oxidised under the influence of, but not as part of, the 

 living bioplasm. 



Pfluger, on the other hand, holds that only what is " living" 

 can be metabolised in the body. For him it is the incoming 

 dead proteid that is stable, and only when it has undergone 

 certain intramolecular changes, which fit it to become the basis 

 of living bioplasm, does it show the characteristic instability that 

 leads to metabolism. All the proteid eaten becomes tissue- 

 proteid before it suffers change. 



The phenomenon which may be called the fundamental 

 phenomenon of proteid metabolism, the rapid elimination of 

 ingested nitrogen — the apparent dependence of proteid utilisation 

 upon proteid supply — was much in favour of Voit's arguments, 

 and has always been hard to reconcile with Pfliiger's view. 

 The latter himself, however, explains it logically enough in 

 this way. Proteid food stands nearest to the living material 

 of the body, and is to be looked upon as the preferential food 

 of the cell for all purposes. So long as enough of it is supplied, 

 the tissues use it to the neglect of fats and carbohydrates, which 

 may thus be stored. Only when so much proteid is available 

 in the day's supply as to be more than enough for all the 

 purposes of the body should we expect to find it stored, and 

 such an amount could not be eaten by man, owing to the 

 organisation of his digestive system. This is a logical con- 

 ception ; but such preference on the part of the cell is almost 

 impossible to prove experimentally, and its probability is much 

 lessened if we deny that all the nitrogen of ingested proteid is 

 built up into the bioplasm before it is excreted. Remembering 

 all that has been said as to the wide diversity of the proteids 

 eaten, and believing that the tissues retain a mean composition 



