AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 97 



illustrate the property of proteins to form salts known as albu- 

 minates, and on this property is based the use of egg albumin as an 

 antidote for poisoning with mercuric chloride or lead salts. 



UREA, URIC ACID AND PURINE BASES 



Urea is one of the end products of the metabolism of protein 

 in the animal body. When body protein, having been built 

 up from food protein, is burned in the body for the production of 

 muscular energy or of body heat, part of the carbon is oxidized 

 to carbon dioxide, part of the hydrogen to water, and the rest 

 of the carbon, hydrogen and oxygen are eliminated through the 

 kidneys in the form of urea, uric acid, creatinine, purine bases 

 (xanthine), etc. These compounds in addition to carbon, 

 hydrogen and oxygen contain all of the nitrogen of the original 

 food or body protein. Their importance in animal physiology 

 is, therefore, apparent. 



Urea 



What now is urea? The composition is CH4N2O and it has 

 been shown to have the constitution of a di-amide of hypothetical 

 carbonic acid. 



/NH2 /OH 



= C<( orHaCOa 



NH2 ^OH 



Urea Carbonic acid 



o=c<; 



The compound may also be defined or considered as amino- 

 formamide. 



H - COOH NH2 - COOH NHo - CO - NH2 



Formic acid Amino-formic acid Amino-formamide 



This constitution may be proven in several ways. Amino- 

 formic acid is the very simplest of the amino-acids. 



H-COOH NH2-COOH 



Formic acid Amino-formic acid 



H 



