20 PHYSIOLOGICAL CHEMISTRY. 



pounds or chlorides. The various organic combinations of 

 chlorine can not replace the salts. It has been pointed out 

 by Bunge that sodium chloride is much more necessary in the 

 food of man or animals consuming a vegetable diet than it is 

 when the diet is mainly flesh. 



Carbonates. The carbonates found in the human body are 

 produced there from the carbonic acid of oxidation. Hard 

 waters contain the carbonates of calcium and magnesium, but 

 these must suffer decomposition when taken into the stomach, 

 and the traces of acid gas so expelled. Besides the carbon 

 dioxide of tissue oxidation we must consider also that formed 

 by several ferment processes in the intestines. A large 

 amount of the gas is produced in this way and part of this 

 is absorbed into the circulation. Under certain conditions the 

 " weak " carbonic acid is able to decompose sodium chloride 

 and produce sodium carbonate and free hydrochloric acid. 

 The origin of the latter in the gastric juice is now accounted 

 for in this way, while the sodium carbonate formed at the 

 same time is carried into the blood and through this to other 

 parts of the body, where other carbonates may be made by 

 double decompositions. The soluble alkali carbonates are the 

 most abundant, but in the bones and in the teeth calcium car- 

 bonate forms an important part. Some carbonates are always 

 excreted by the urine, and the alkali-earth carbonates may 

 occasionally appear in the sediment. 



Sulphates. Sulphur may enter the body in a variety of 

 combinations but nearly all of it is finally excreted in the 

 completely oxidized form, that is, as sulphates, by the urine. 

 Sulphur in organic combination is found in all protein sub- 

 stances and in the final oxidation of these compounds in the 

 body sulphuric acid is produced. The manner in which this 

 is combined before excretion will be discussed later. The 

 amount of sulphur normally present in the body is but a 

 small fraction of one per cent of the weight of the latter and 

 practically all of it is found in the protein or protein-like sub- 

 stances. Among these keratin is characterized by its rela- 



