190 PHYSIOLOGICAL CHEMISTRY 



The whole subject of the role and formation of the creatine of 

 the tissues and the formation of creatinine is still in a very un- 

 satisfactory state, although it appears evident that these sub- 

 stances are intimately connected with endogenous tissue metab- 

 olism itself, with the actual wear and tear of the tissue sub- 

 stance. 



Creatinine occurs in the blood, and increases in amount in 

 nephritis. A value of 5 mg. per 100 c.c. blood is called the 

 fatal ratio, since, if it reaches this level the patient rarely re- 

 covers. 



Inorganic Constituents 



The urine contains a variety of inorganic constituents 

 such as chlorides, sulphates, phosphates, carbonates, etc., 

 of sodium, potassium, calcium and magnesium. In addition, 

 various others occur. There are traces of nitrates, believed to 

 come mainly from nitrates in the drinking water. Iron also is 

 found in traces, about 8-10 mg. per day. It probably is both in 

 inorganic and organic compounds. Fluorides, silicic acid and 

 other substances also occur, as well as accidental constituents 

 taken with the food. 



Chlorides. Of the inorganic constituents, chlorides make up 

 the largest part. Sodium chloride is present in greatest amount, 

 and the total chlorides of the urine usually are reported as 

 ''sodium chloride." The total amount averages 10-15 grams of 

 sodium chloride a day, but it may vary greatly, the variation de- 

 pending chiefly on the amount of "salt" in the diet. Drinking 

 much water will increase the chloride output. The excretion is 

 greater during activity than at night. The amount decreases in 

 some diseases, as during the formation of exudates in pneumonia. 

 When reabsorption takes place after the crisis, the retained 

 chloride reappears in the urine. It is interesting that sodium 

 chloride is the only salt present in an ordinary mixed diet in 

 amounts insufficient for the body's needs. It must be added to 

 the food. The well known salt craving of herbivorous animals 



