648 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 

 is given in the accompanying table. 



NITROGEN-RICH DIET NITROGEN-POOR DIET 



Volume of urine 1170 c.c. 385 c.c. 



Total nitrogen 16.8 grams 3.60 grams 



Urea nitrogen 14.7 grams = 87.5% 2.20 grams = 61.7% 



Ammonia nitrogen 0.49 gram 3.0% 0.42 gram = 11.3% 



Uric-acid nitrogen 0.18 gram 1.1% 0.09 gram 2.5% 



Creatinine nitrogen 0.58 gram 3.6% 0.60 gram 17.2% 



Undetermined nitrogen 0.85 gram = 4.9% 0.27 gram 7.3% 



Total SO 3 3.64 grams 0.76 gram 



Inorganic SO 3 3.27 grams =90.0% 0.46 gram =60.5% 



Ethereal SO 3 0.19 gram = 5.2% 0.10 gram =13.2% 



Neutral SO 3 0.18 gram = 4.8% 0.20 gram =26.3% 



(Folin.) 



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 nitrogen is not borne proportionately by all of 

 the metabolites. This is seen by examination of the percentage figures 

 which are obtained by calculating the nitrogen of each substance as a 

 percentage of the total nitrogen. The urea decreases relatively much 

 more than the total nitrogen. The inorganic sulphate 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. 



The most striking results of the above investigation are that creatinine 

 remains unchanged during starvation^ but that urea becomes relatively 



