UREA 339 



Composition of the Urine. Regarding the excrementitious constitu- 

 ents of the urine as a measure, to a certain extent, of the general 

 processes of katabolism, it is more important to recognize the quantities 

 of these products discharged in a definite time than to learn simply their 

 proportions in the urine ; and in the preceding table of composition of 

 the urine, the absolute quantities of its different constituents excreted 

 in twenty-four hours have been given when practicable. 



Urea. As regards quantity, and probably as a measure of the 

 activity of the process of proteid katabolism, urea CO(NH 2 ) 2 is 

 the most important of the urinary constituents. Regarding the daily 

 excretion of urea as a measure of the physiological wear of certain 

 tissues, its consideration would come properly under the head of nu- 

 trition, in connection with other substances known to be products of 

 katabolism ; but it is convenient to treat of its general physiological 

 properties and some of its variations in common with other excrementi- 

 tious matters separated by the kidneys, in connection with the composi- 

 tion of the urine. 



The formula for urea, showing the presence of a large proportion of 

 nitrogen, would lead to the supposition that this substance is one of the 

 products of the wear of the nitrogenous constituents of the body. It is 

 found, under normal conditions, in the urine, the lymph and chyle, the 

 blood, the sweat, the vitreous humor and a trace in the saliva. Its 

 presence has been demonstrated, also, in the substance of the healthy 

 liver in both carnivorous and herbivorous animals ; and it has been 

 found in minute quantity in the muscular juice. 



Urea has been produced synthetically by combining ammonium 

 sulphate with potassium. The products of this combination are potas- 

 sium sulphate, with cyanic acid and ammonium in a form to consti- 

 tute urea. . Ammonium cyanate is isomeric with urea, and the change 

 is effected by a rearrangement of its elements. It has long been known 

 that urea is readily convertible into ammonium carbonate ; and ammo- 

 nium carbonate, when heated in sealed tubes to the temperature at which 

 urea begins to decompose, is converted into urea. 



Urea may readily be extracted from the urine by processes fully 

 described in works on physiological chemistry ; and its proportion 

 may now easily be estimated by the various methods of volumetric 

 analysis. It is not so easy, however, to separate it from the blood or 

 from the substance of any of the tissues, on account of the difficulty in 

 getting rid of other organic matters and the readiness with which it 

 undergoes decomposition. 



When pure, urea crystallizes in the form of long, four-sided, colorless 

 and transparent prisms, which are without odor, neutral, and in taste 



