486 



VICTOR C. MYEES 



60 per cent is ordinarily organic and the remainder inorganic. Since the 

 organic constituents of urine are chiefly nitrogenous and since the nitro- 

 genous waste products are eliminated principally in the urine, i.e., to the 

 extent of 85 to 90 per cent, a study of their elimination in the urine 

 under different conditions of diet should furnish considerable insight 

 into the controlling factors in protein metabolism. 



The most satisfactory discussion of this subject has been given by 

 Folin(&) in his now classic papers published in 1905. With the aid of 

 many new methods which he'had developed, Folin found it possible to make 

 fairly complete analyses of single 24 hr. specimens of urine. By a study of 

 the comparative distribution of the nitrogenous compounds in the urine on 

 two diets, one containing rather more than 100 grams of protein and 

 the other (starch-cream) containing about 1 gram of nitrogen, he was 

 able to differentiate between the endogenous and exogenous origin of the 

 different waste products. As a result of these observations he evolved a 

 new theory "of protein metabolism, which quickly supplanted the un- 

 tenable theories of Pfliiger and Voit. 



The important components of the total nitrogen of the urine are the 

 nitrogen of the urea, creatinin, ammonia and uric acid. The following 

 data taken from Folin illustrate the distribution of these compounds (like- 

 wise the various sulphur compounds which are also derived from the 

 protein) in the urine of the same individual on a high and on a low 

 protein diet. 



From the above data it is apparent that the distribution of the nitrogen 

 in the urine among urea and the other nitrogenous constituents depends 

 on the absolute amount of total nitrogen present (the distribution of the 

 sulphur likewise being dependent upon the amount, of the total sulphur). 

 As will be noted urea is the only nitrogenous substance which suffers a 

 relative as well as an absolute diminution with a decrease in the total 

 protein metabolism. On the other hand, as Folin was the first to point 

 out, the absolute quantity of creatinin eliminated in the urine on a 

 meat free diet is a constant quantity, different for different individuals, 



