CHEMISTRY OF URINE 



485 



The sulphur of the inorganic sulphates is the fraction of the total 

 sulphur which fluctuates in proportion to the total protein metabolism. 

 In this regard it follows the variations in the urea. It represents 

 ' exogenous ' metabolism. The neutral sulphur occupies a position 

 analogous to that of the creatinin : the smaller the amount of protein 

 in the food, and the smaller therefore the total protein decomposed, the 

 larger is the fraction which the neutral sulphur forms of the total 

 sulphur. The neutral sulphur accordingly represents endogenous 

 metabolism. The ethereal sulphur takes an intermediate position in 

 this regard, but upon the whole it also becomes a more prominent 

 fraction of the total sulphur when the food contains little or no protein. 

 The ethereal sulphates are therefore not entirely derived from the 

 putrefaction of protein. 



Carbonates of sodium, ammonium, calcium, and magnesium occur 

 in alkaline urine. Their source is the carbonates and the vegetable 

 organic acids of the food. In acid urine a certain amount of carbon 

 dioxide is present, although not firmly united with bases, so that most 

 of it can be pumped out. 



So-called Physico-Chemical Analysis of Urine. The freezing-point 

 of urine has often been determined to obtain a measure of the mole- 

 cular concentration, which with the total quantity of urine secreted 

 in a given time was erroneously assumed to afford an index of the 

 work done by the kidney. Clinically the method is of little use, but 

 for certain physiological questions freezing-point determinations are 

 of value and are sometimes combined with determinations of the 

 electrical conductivity, by which we obtain an approximate measure 

 of the number of dissociated ions in unit volume, mainly the inorganic 

 salts. Normally, A has a higher value for urine than for blood i.e., 

 the molecular concentration of the urine is higher than that of the 

 serum. But when large draughts of water are taken A may be lower 

 for urine than for blood, and in general it varies within far wider 

 limits (from 0-115 to 2-546 C., according to Koppe). The following 

 table from Kovesi and Roth-Sch,ulz shows the changes in A under the 

 influence of water : 



The Urine in Disease. Although, strictly speaking, a truly patho- 

 logical urine has no place in physiology, the line which separates the 

 urine of health from that of disease is often narrow, sometimes invisible ; 

 while the study of abnormal constituents is not only of great importance 

 in practical medicine, but throws light upon the physiological processes 



