CHEMIC COMPOSITION OF THE HUMAN BODY 21 



the blood, from which they are finally eliminated, along with the water in 

 which they are dissolved. A portion of the water is chemically combined 

 with other tissue constituents and gives to the tissues their characteristic 

 physical properties. The consistency, elasticity, and pliability are, to a 

 large extent, conditioned by the amount of water they contain. The total 

 quantity of water eliminated by the kidneys, lungs, and skin amounts to 

 about 3 kilograms (6$ pounds) daily. 



CALCIUM COMPOUNDS. 



Calcium phosphate, Ca 3 (PO 4 ) 2 , has a very extensive distribution 

 throughout the body. It exists largely in the bones, teeth, and to a slight ex- 

 tent in cartilage, blood, and other tissues. Milk contains 0.27 per cent. 

 The solidity of the bones and teeth is almost entirely due to the presence of 

 this salt, and is, therefore, to be regarded as necessary to their structure. 

 It enters into chemic union with the organic matter, as shown by the fact 

 that it cannot be separated from it except by chemic means, such as immer- 

 sion in hydrochloric acid. Though insoluble in water, it is held in solution 

 in the blood and milk by the protein constituents, and in the urine by the 

 acid 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 situa- 

 tions in the body as the phosphate, and plays essentially the same r61e. 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. 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. 



Sodium chlorid also influences favorably the general nutritive process, 

 though the manner in which it acts is not very clear. During its existence 

 in the body it undergoes chemic transformations or decompositions, yielding 

 its chlorin 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 



