ELEMENTARY PHYSIOLOGICAL CHEMISTRY 247 



Measure out 5 c.c. of the solution with a pipette, place it in the dis- 

 tilling flask A, dilute to 200 c.c. with water. Now measure accurately 



20 c.c. -^- acid and place in receiving flask B, adjust distilling tube , 



neutralise contents with NaOH, and distil as above. 



The total amount of nitrogen excreted by the urine per diem 

 varies between 15 grammes and 20 grammes, and if the total 

 amount taken as food be ascertained it will be found to nearly corre- 

 spond to this. By special precautions it can be made to accurately 

 correspond when the person is said to be in nitrogenous equilibrium. 

 The excretion during starvation will be discussed under Urea. 



The Nitrogenous Compounds. The nitrogen excreted in the urine 

 is distributed in the various compounds in the following proportions : 



Urea, - 86 per cent. 



Ammonia, - 3 ,, 



Creatinin, - 3 



Uric acid and purin bodies, - 2 



Pigments, nucleo-albumin, hippuric acid, etc., 6 ,, 



As will be pointed out later, the relationship of ammonia to urea is of 

 great importance, since, in certain diseases of the liver, it becomes 

 changed, relatively more ammonia being excreted. 



CHAPTER XVI. 

 UREA : CHEMICAL RELATIONSHIPS. 



UREA is a di-amide of carbonic acid. When studying the decom- 

 position products of proteids (see Intestinal Digestion) we came 

 across amido acids, in which an H atom of the methyl radicle was sub- 

 stituted by an amido group NH 2 . If, now, the hydroxyl OH 

 radicle of the carboxyl COOH be replaced by NH 2 , a body called an 

 acid amide is produced. Take acetic acid, CH 3 COOH, and its amido 

 acid has the formula, CH 2 NH 2 COOH, and its acid amide, CH 3 CONH 2 . 

 Urea is closely related to an acid amide. Carbonic acid has the 



QTT 



formula C0<r)jj ; if> now, we substitute both hydroxyl radicles by an 

 amido group we obtain CO<\TTT 2 , which is urea. s Since this contains 



two ammonia residues it manifests weak basic properties, and forms 

 loose salts with nitric and oxalic acids. 



