112 PHYSIOLOGY FOR DENTAL STUDENTS. 



from the dietary such foodstuffs as meats and sweetbreads, which 

 yield exogenous purins. As we have said, there is no reason to 

 believe that any other diseases besides gout are due to excess of 

 uric acid in the blood. 



Besides the above there are traces of other nitrogenous sub- 

 stances in the urine, such as : 



1. Hippuric acid, which, as its name signifies, is very abun- 

 dant in the urine of the horse and other herbivora, and which is 

 the excretory product of the aromatic substances which the food 

 of these animals contains. 



2. Cystin, an amino acid containing sulphur. 



3. Pigments and mucin. 



The exact significance of the end products of nitrogenous met- 

 abolism has been very beautifully demonstrated by Folin, of 

 Harvard. The observations were made on several men who lived 

 for some days on a diet rich in protein (but containing no purin- 

 containing foodstuffs), and then on one which was very poor in 

 protein. The problem was to see how each of the nitrogenous 

 constituents behaved during the two periods, both absolutely 

 and in relation to the total amount of nitrogen excreted. In or- 

 der to show the latter relationship the results are given, as in the 

 following table, not as urea, etc., but as urea-nitrogen, etc. : 



On the protein-rich On the protein- 

 diet poor diet 



Quantity of urine 1170 c. c. 385 c. c. 



Total nitrogen 16.8 gr. 3.6 gr. 



Urea-nitrogen 14.7 gr. (87.5) 2.2 gr. (61.7) 



Ammonia-nitrogen 0.49 gr. (3.0) 0.42 gr. (11.3) 



Uric acid-nitrogen 0.18 gr. (1.1) 0.09 gr. (2.5) 



Creatinin-nitrogen 0.58 gr. (3.6) 0.60 gr. (17.2) 



Undetermined nitrogen . . . 0.85 gr. (4.9) 0.27 gr. (7.3) 



The figures in parentheses represent the percentage which the 

 nitrogen of, each substance furnishes of the total amount of nitro- 

 gen excreted. It will be seen that urea decreases on the poor 

 diet relatively more than total nitrogen, thus indicating that it 

 comes partly from proteins in the food (exogenous) and partly 



