322 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 



Sodium phosphate, Na 2 HP0 4 , is found in all the solids 

 and fluids of the body, giving an alkaline reaction to the 

 latter. It is associated with potassium phosphate, K2HPO4, 

 with similar properties. 



2. Compounds of Potassium. — Potassium chloride, KC1, 

 occurs together with sodium chloride in all the tissues and 

 fluids of the body, being present, however, to a greater 

 extent in the tissues than in the fluids. 



Potassium carbonate, K2CO3, is found with potassium 

 phosphate, which is mentioned above. 



3. Compounds of Calcium. — Calcium phosphate, mentioned 

 above. 



Calcium carbonate, CaCOs, occurs together with calcium 

 phosphate in various parts of the body, and fulfills appar- 

 entlv the same functions. In the tissue fluids it occurs as a 

 bicarbonate, CaH 2 (C03)2- 



Calcium fluoride, CaF 2 , is found in the bones and teeth. 



4. Compounds of Iron are organic in nature, occurring in 

 haemoglobin, in the lymph, bile, gastric juice, and in the 

 coloring matter of the ej^es, hair, and skin. 



5. Compounds of Sodium. — Sodium chloride, NaCl, is 

 present in all the tissues and fluids of the body, particularly 

 in the latter. The blood contains 0.6 per cent., lymph 

 0.5 per cent. Its function apparently is to maintain osmotic 

 equilibrium between the cells and the fluids of the body, 

 regulating the intake of water to the former. In pure water 

 the tissue cells swell rapidly and die. The presence of sodium 

 chloride in water prevents too rapid entrance of water 

 to the cells. On this account in investigating living tissue 

 it is customary to use a physiological salt solution which 

 is a 0.6 per cent, solution of sodium chloride. Sodium 

 chloride is also the source of chlorine for potassium chloride 

 mentioned above and also for the hydrochloric acid of the 

 gastric juice mentioned below. 



Sodium phosphate, mentioned above. 



Sodium carbonate, Na 2 C0 3 , found together with sodium 

 phosphate, and serves also to give alkalinity to the tissue 

 fluids. When combined with carbon dioxide it exists in the 

 form of sodium bicarbonate, Na 2 HC0 3 . 



