COMPOSITION AND CHARACTERS OF URINE 1243 



stituents of the body fluids, it does not seem that the chlorides enter 

 into organic combination with the constituents of the cells. The 

 output of chlorides, which normally varies from 6 to 10 grm. in the 

 course of the day, will therefore depend on the amount of chlorides 

 taken in with the food. If these be withdrawn altogether, the chlorides 

 may almost disappear from the urine, although the circulating 

 blood contains practically the same amount of chlorides as in the 

 normal individual, showing that the body retains the chlorides neces- 

 sary for the proper carrying out of the vital processes as long as possible. 

 Chlorides may also disappear from the urine temporarily under various 

 pathological conditions. This is especially marked in cases of acute 

 pneumonia. 



Sulphates. The salts of sulphuric acid do not form an important 

 constituent of the food. The sulphates of the urine are derived almost 

 entirely from the oxidation of the sulphur of the protein molecule. 

 The output of sulphates is therefore, like that of urea, an index of 

 protein metabolism. As the nitrogen of the urine goes up, so 

 the sulphates will increase. On an average diet the ratio of urinary 

 nitrogen to S0 3 is about 5:1; though, owing to the varying content 

 of different proteins in the sulphur, this ratio will naturally alter with 

 the nature of the protein taken as food. The daily output of sulphuric 

 acid varies between 1-5 and 3 grm. S0 3 . The greater part of the 

 sulphate is present as sulphates of the alkaline metals. A certain 

 proportion, about 10 per cent., is present in the form of conjugated 

 or ethereal sulphates, chiefly indoxyl sulphate. A small proportion 

 of the sulphur excreted in the urine is present in unoxidised form as 

 so-called neutral sulphur. The neutral sulphur probably includes 

 a number of different bodies, among which sulphocyanates and cystine 

 are the best known. 



Inorganic sulphates can be precipitated from the urine by the addition 

 of hydrochloric acid and barium chloride. On filtering off this precipitate, the 

 filtrate contains the ethereal sulphates. On boiling, the hydrochloric acid decom- 

 poses these substances, setting free sulphuric acid, which combines with the 

 excess of barium present and is precipitated as barium sulphate. This second 

 precipitate therefore, when weighed, gives the amount of ethereal sulphates 

 present. To determine the neutral sulphur the fluid, after the separation of 

 both kinds of sulphates, is treated with sodium carbonate to precipitate the 

 barium, filtered, and the filtrate evaporated to dryness. The residue is then 

 ignited with potassium nitrate, cooled, and extracted with water. By this treat- 

 ment all the neutral sulphur is converted into sulphates, which can be thrown 

 down from the solution with barium chloride and weighed in the usual way. 



Phosphates. The phosphates of the urine are derived partly from 

 the phosphates of the food, partly from the oxidation of the organic 

 phosphorus-containing constituents of the food and of the tissues, 

 e.g. nuclein, lecithin, &c. If the food contains much calcium 



