PROTEIN METABOLISM 95 



sented by kreatinin and neutral sulphur, and to a less 

 extent by uric acid and ethereal sulphates. The more 

 the total catabolism is reduced, the less prominent be- 

 come the two chief representatives of the variable 

 catabolism." 



"The fact that the urea and inorganic sulphates 

 represent chiefly the variable catabolism does of course 

 not preclude the possibility that they also represent to 

 some extent the constant catabolism." 



In accordance with these two types of catabolism 

 Folin has furnished suitable names. The protein 

 metabolism which tends to be constant is tissue metab- 

 olism, or endogenous metabolism ; the other, the vari- 

 able protein metabolism, is the exogenous or inter- 

 mediate metabolism. 



Instead of assuming, as did Voit and Pfliiger, that 

 the same type of decomposition, i.e., oxidation, occurs 

 with protein as with fats and carbohydrates, Folin 

 advances the view that the disintegration of protein 

 in catabolism is produced in large measure by a series 

 of hydrolytic splittings, nitrogen being split off as 

 ammonia. 



It is further shown that contrary to the ideas of 

 Voit and Pfliiger, extensive formation of urea does 

 not occur in the muscles. Folin believed (1905) that 

 the nitrogenous cleavage products formed in the ali- 

 mentary canal from food protein are denitrogenized, 

 probably in the intestine, the ammonia split off, carried 

 to the liver, built up into urea and eliminated. The 

 non-nitrogenous residue is in part converted into 



