CHEMIC COMPOSITION OF THE HUMAN BODY. 23 



extent 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 can not be separated from it except by chemic means, such as hydro- 

 chloric 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 for- 

 mation 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 fluorid, 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 percent. 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. 



Sodium chlorid also influences the general nutritive process, increasing 

 the disintegration of the proteids, as shown by the increased amount of urea 

 excreted. During its existence in the body it undergoes some chemic 

 transformations or decompositions, yielding its chlorid to form 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. 



