94 THE PHYSIOLOGY OF PROTEIN METABOLISM 



Folin. 



Folin (i 3 1), in 1905, advanced an extremely interesting and valuable 

 theory based on the laws which governed the composition of the urine. 

 He carried out a very elaborate series of analyses of normal urine 

 obtained from subjects on standard diets, (i) rich in nitrogen, and (2) 

 poor in nitrogen, both diets being practically free from purine, creatine 

 and creatinine. He said that there were two forms of catabolism 

 which were essentially independent and quite different " One kind is 

 extremely variable in quantity, the other tends to remain constant. 

 The one kind yields chiefly iirea and Anorganic sulphates, no creatinine 

 and probably no neutral sulphur. The other, the constant catabolism, 

 is largely represented by creatinine and neutral sulphur, and to a less 

 extent by^uric acid and ethereal sulphates!) The more the total cata- 

 bolism is reduced the more prominent become these representatives of 

 the constant catabolism, the less prominent become the two chief re- 

 presentatives of the variable catabolism." To the constant type he 

 has given the name of tissue or endogenous metabolism, and to the 

 variable intermediate or exogenous metabolism. The following table 

 of Folin's demonstrates his views very clearly: 



Folin held that the arguments advanced for the immediate resyn- 

 thesis hypothesis of absorbed protein were not valid, as they were based 

 on purely teleological grounds. He considered that his observations 

 necessarily led to the view that only a small amount of protein was 

 required by the organism, namely that necessary for the endogenous 

 metabolism. He was further inclined to accept the evidence put for- 

 ward by Chittenden as incontrovertible. He overlooks, however, the 

 essential fact regarding protein requirements that in all probability it is 

 not so much the quantity as the quality of the food provided which is 

 of importance, so long as we have not a perfect food supply, i.e. food 



