SUBSTANCES WHICH PASS THROUGH THE ORGANISM. 433 



constant. This is another fact in favor of the view that the presence of a 

 definite quantity of common salt in the circulating fluid is essential to normal 

 nutrition. 



Origin and Discharge of Sodium Chloride. Sodium chloride is always 

 introduced with food, in the condition in which it is found in the body. It 

 is contained in the substance of all kinds of food, animal and vegetable ; but 

 in the herbivora and in man, this source is not sufficient to supply the wants 

 of the system, and it is introduced, therefore, as salt. The quantity which is 

 discharged from the body has been estimated by Barral to be somewhat less 

 than the quantity introduced, about one-fifth disappearing ; but these esti- 

 mates are not entirely accurate, for the quantity thrown off in the perspira- 

 tion has never been directly ascertained. It exists in the blood in connection 

 with potassium phosphate, and a certain quantity is lost in a double decom- 

 position which takes place between these two salts, resulting in the forma- 

 tion of potassium chloride and sodium phosphate. It also is supposed to 

 furnish sodium to all the salts which have a sodium base, and a certain quan- 

 tity, therefore, disappears in this way. 



Existing, as it does, in all the solids and fluids of the body, sodium chlo- 

 ride is discharged in all the excretions, being thrown off in the urine, faeces, 

 perspiration and mucus. 



Potassium Chloride. Potassium chloride, although neither so important 

 as sodium chloride nor so generally distributed in the economy, seems to 

 have analogous uses. It is found in the muscles, liver, milk, chyle, blood, 

 mucus, saliva, bile, gastric juice, cephalo-rachidian fluid and urine. It is 

 very soluble, and in these situations it exists in solution in the fluids. Its 

 quantity in the fluids has not been accurately ascertained, as it has gen- 

 erally been estimated in connection with sodium chloride. In the muscles 

 it exists, however, in a larger proportion than common salt. In cow's milk, 

 Berzelius found 1-7 part per 1,000. Pfaff and Schwartz found T35 per 

 1,000 in cow's milk and - 3 per 1,000 in human milk. Of the uses of this 

 salt, little remains to be said after what has been stated with regard to sodi- 

 um chloride. The uses of these two salts are probably identical, although 

 sodium chloride, on account of its greater quantity in the fluids and its uni- 

 versal distribution, is by far the more important. 



Origin and Discharge of Potassium Chloride. This substance has two 

 sources ; one in the food, existing, as it does, in muscular tissue, milk etc., 

 and the other in a chemical reaction between potassium phosphate and sodi- 

 um chloride, forming potassium chloride and sodium phosphate. That this 

 decomposition takes place in the body, is evident from the fact that the in- 

 gestion of a considerable quantity of common salt has been found, in the 

 sheep, to increase the quantity of potassium chloride in the urine, without 

 having any influence upon the quantity of sodium chloride. Potassium chlo- 

 ride is discharged from the body in the urine and in mucus. 



Calcium Phosphate. This salt is found in all the solids and fluids of the 

 body. As it is always united, in the solids, with organic substances as an 

 important element of constitution, it is hardly second in importance to water. 



