614 METABOLISM 



excretion of the sulphur moiety of the protein molecule, for it will be 

 remembered that it is in protein alone that sulphur is usually taken into 

 the animal body. The excretion of sulphur therefore runs more or less 

 parallel with the intensity of protein metabolism. 



After selecting the end products that are most likely to be of signif- 

 icance, the first question concerns the amount of each of them excreted 

 during twenty-four hours on diets that are either rich or poor in pro- 

 tein. The possibility of conducting such investigations obviously de- 

 pends on the use of quick and yet reliable methods for the estimation 

 of the nitrogenous metabolites. Such methods have been furnished by 

 the painstaking and careful work of Folin, an example of whose results 

 are given in the accompanying table. 



The general conclusions which may be drawn from these results are 

 as follows: 



1. With a protein-rich diet much more urine is excreted in twenty- 

 four hours than with one that is protein-poor. Evidently the nitrogenous 

 metabolites act as diuretics. 



2. The total or absolute amounts of nitrogen and of all the other 

 nitrogenous metabolites, save creatinine, become diminished during the 

 starvation period. The same is true of the sulphur derivatives, except 

 in the case of the neutral sulphur, which behaves like creatinine. 



3. The decrease in the portion of nitrogen excreted as urea is relatively 

 greater than the decrease in total nitrogen, this fact being shown in the 

 table by the percentage figures, which were secured by calculating 

 the proportion of nitrogen in the various substances as a percentage 

 of the total nitrogen excreted during the periods. The inorganic sul- 

 phate behaves in a manner similar to the urea that is, the percentage 

 of total sulphate excreted in the inorganic form becomes much less 

 during starvation. 



4. The relative amount of all the other nitrogenous metabolites, as 

 well as that of the ethereal and neutral sulphates, becomes increased 

 during starvation. 



