CHEMICAL COMPOSITION OF THE HUMAN BODY 17 



The most important salts of the body are : 



1 . Sodium chloride (common table-salt). This is chiefly 

 found in the fluids of the tissues (o.6#); to a lesser extent, 

 in the cells. It serves as a solvent for certain proteids 

 (globulin) and supplies the osmotic pressure of the body fluid 

 which keeps in equilibrium the osmotic pressure of the cells. 

 This prevents the entering of water into the cells. In pure 

 water, all tissue cells die, swelling rapidly. For this reason, 

 in the investigations of living tissue, the so-called physio- 

 logical salt solution (0.6$ NaCl) is used. From the sodium 

 chloride, the gastric mucosa forms the hydrochloric acid of 

 the gastric juice. 



2. Potassium chloride is the most important chlorine 

 compound in the cells and serves to maintain the osmotic 

 equilibrium. In the body fluids it is found in but small 

 quantities and is not of any special physiological significance. 



3. Sodium carbonate is chiefly found in the tissue fluids 

 (0.2-0.3$). It imparts to these fluids their alkaline reaction 

 and basic nature. 



4. Bicarbonate of sodium is also found in the tissue fluids ; 

 it is the carrier of the carbonic acid formed by combustion in 

 the body. (See Chapter III.) 



5 . Potassium phosphate (probably the secondary) is an 

 important constituent of all cells. It is the most abundant 

 salt in the cells. It is doubtful whether the salt is merely 

 dissolved in the fluids of the cells or is united with their 

 organic constituents. 



6. Neutral calcium carbonate forms a part of the salts of 

 bones, builds the otoliths of the ear, and perhaps also the 

 crystals of the spermatic fluid. 



7. Acid calcium carbonate is dissolved in the tissue fluids. 

 It readily yields carbonic acid and is therefore, like bicarbon- 

 ate of sodium, of importance as a carrier of carbon dioxide 

 in the exchange of gases in respiration. 



8. Neutral calcium phosphate is the chief mineral con- 

 stituent of the skeleton, of which it forms one-fifth by weight. 



9. Acid calcium phosphate is dissolved in the tissue 



