230 PHYSIOLOGY FOB DENTAL STUDENTS. 



tained from the results of the analysis of a number. of normal 

 average urines, show how the nitrogen is distributed among these 

 compounds. 



Urea 85 to 90'/ 



Ammonia 2 to 4% 



Creatinin 3% 



Uric acid 1 to 2% 



Unclassified nitrogen 5 to 6% 



Urea. From the above figures it is seen that the greater part 

 of the nitrogen eliminated by man appears as urea. The relative 

 amount of urea eliminated depends very largely on the diet, be- 

 ing 90 per cent or more of the total nitrogen excretion on a full 

 protein diet, and 60 per cent or less during starvation. The total 

 amount excreted is about 30 grams per 100 grams of protein in 

 the diet 7 . 



Chemically urea has the following formula: 



NH., 



/ 

 OC 



NH 2 



If prepared pure it forms long colorless needles or four-sided 

 prisms. It is very soluble in water. Hot alkalies, such as sodium 

 hydoxide, decompose it into ammonia and carbon dioxide. The 

 same reaction occurs in case of bacterial decomposition by the 

 micrococcus urea, and accounts for the ammonical odor of urine 

 after standing in the air. The significance of urea in regard to 

 protein metabolism and the method of its formation are dis- 

 cussed on page 108. 



Ammonia. This, combined with chlorine or other acid radi- 

 cles, is normally found in small amounts in the urine. It is one 

 of the important agencies in maintaining the neutrality of the 

 tissues, since with acids it forms ammonia salts, which are neu- 

 tral in reaction and which are eliminated in the urine. 



Creatinin. The amount of this substance found in the urine 



