38 TEXT-BOOK OF PHYSIOLOGY. 



phosphate of soda. The total quantity of calcium phosphate which 

 enters into the formation of the body has been estimated at 2.5 

 kilograms. The amount eliminated daily from the body has been 

 estimated at 0.4 gm., a fact which indicates that nutritive changes 

 do not take place with much rapidity in those tissues in which it is 

 contained. 



Calcium carbonate, CaCO 3 , is present in practically the same 

 situations in the body as the phosphate, and plays essentially the 

 same role. It is, however, found in the crystalline form, aggregated 

 in small masses in the internal ear, forming the otoliths, or ear stones. 

 Though insoluble, it is held in solution by the carbonic acid diffused 

 through the fluids. 



Calcium fluorid, CaF 2 , is found in bones and teeth. 



SODIUM COMPOUNDS. 



Sodium chlorid, NaCl, is present in all the tissues and fluids 

 of the body, but especially in the blood, 0.6 per cent., lymph, 0.5, 

 and pancreatic juice, 0.25 per cent. The entire quantity in the body 

 has been estimated at about 200 gm. Sodium chlorid is of much 

 importance in the body, as it determines and regulates to a large 

 extent the phenomena of diffusion which are there constantly taking 

 place. This is illustrated by the fact that a solution of albumin 

 placed in the rectum without the addition of this salt will not be 

 absorbed. When the salt is added, absorption takes place. The 

 ingested water is absorbed into the blood largely in consequence of 

 the percentage of this salt which it contains. The normal percentage 

 of sodium chlorid in the blood-plasma assists in maintaining the shape 

 and structure of the red blood-corpuscles by determining the amount 

 of water entering into their composition. The same is true of other 

 tissue elements, v 



Sodium chlorid also influences the general nutritive process, in- 

 creasing the disintegration of the proteids, as shown by the increased 

 amount of urea excreted. During its existence in the body it under- 

 goes chemic transformations or decompositions, yielding its chlorid 

 to form the potassium chlorid of the blood-corpuscles and muscles 

 and to form the hydrochloric acid of the gastric juice. 



Sodium phosphate, Na 2 HPO 4 , is found in all solids and fluids 

 of the body, to which, with but few exceptions, it imparts an alkaline 

 reaction. This is especially true of blood, lymph, and tissue fluids 

 generally. It is essential to physiologic action that all tissue elements 

 should be bathed by an alkaline medium. 



Sodium carbonate, Na 2 CO 3 , is generally found in association 

 with the preceding salt. As it is an alkaline compound, it also 

 assists in giving to the blood and lymph their characteristic alkalinity. 

 In carnivorous animals the sodium phosphate is the more abundant, 



