CH. XII.] CHLORIDES AND SULPHATES. 281 



Anions. 



Chlorides form the chief part of the anions of the 

 urine. The amount excreted is often calculated as if it all 

 existed as NaCl, though the amount of sodium in the urine 

 is normally not sufficient to combine with all the chlorine. 

 The amount in the urine depends largely on the amount in 

 the food, but since an important function of the kidney is 

 to maintain a constant osmotic pressure of the tissue 

 fluids, mainly by variations in the amount of NaCl excreted, 

 it follows that anything tending to cause a change in the 

 osmotic equilibrium in the body is liable to alter the 

 excretion of chlorides in the urine. 



Thus during starvation and during the formation of 

 exudates in pneumonia the chlorides may disappear from 

 urine. The amount of Cl excreted per diem is about 7 

 grams. Reckoned as NaCl it is 12 grams. 



For the method of estimation see p. 352. 



Sulphates. Only a small portion of the sulphate 

 excreted in the urine is taken in as such with the food. 

 The greater portion is derived from the oxidation of sulphur 

 containing substances, chiefly proteins. The amount 

 of sulphates is thus a rough measure of the total amount 



N ^ 



of protein metabolised, the ratio - being usually - 



SO 3 i 



Sulphates are excreted very rapidly after a protein 

 meal, reaching a maximum about the third hour. This 

 seems to indicate that cystine, the sulphur complex of 

 proteins, is split off and absorbed very early in the digestion 

 of proteins. 



Ethereal Sulphates are esters formed by the union of 

 sulphuric acid with phenols. 



O OH O O.C 6 H 5 



\/ V/ 



S + HO.C 6 H 5 => g + H 2 



<f\ X x \ 



O OH O OH 



Sulphuric acid- Phenol. Phenyl sulphuric acid. 



