CHEMICAL COMPOSITION OF THE HUMAN BODY 15 



The physiological importance of water is as follows : 



(a) It serves as a solvent and as such it renders possible 

 physical and chemical processes such as diffusion, mechanical 

 movement, and the chemical action of dissolved substances. 



(b) As a means of imbibition, which determines the semi- 

 solid consistency of the tissues. 



(c) By evaporation from the lungs and body surface, it 

 takes heat from the body and, hence serves as a tempera- 

 ture regulator. 



(</) It takes part in chemical processes, e.g. in the 

 hydrolytic splitting up. 



2. Bases are not found in a free state but, united with 

 acids, are present in the form of salts. As more than suffi- 

 cient acids are present for the union with bases, acid salts 

 are formed. Under certain conditions the existence of a free 

 acid must be granted, namely, carbonic acid. Hydro- 

 chloric acid is found in a free state in the gastric juice ; it is 

 set free from sodium chloride by the gland-cell of the 

 mucosa. 



3. Salts, formed by the union of acids and bases, in which 

 the hydrogen of the acid is replaced by the metal of the 

 base, are present in the body to a large extent. When the 

 tissue is burned the salts remain behind as ash. The ash, 

 however, is not identical with the original salts of the body, 

 as, by the incineration of the body, substances appear in the 

 ash which were not present in that form in the organism. 

 Originally they were present in organic compounds, e.g. 

 iron as a constituent of haemoglobin ; part of the sulphuric 

 and phosphoric acids were derived from the proteid, lecithin, 

 and nucleins. On the other hand, certain salts originally 

 present, as acid carbonates or phosphates, are converted 

 into neutral salts by combustion. Very often the salts can 

 be investigated only after the incineration of the tissue, 

 therefore the ash and its constituents must be taken into 

 consideration in studying the composition of the body. 



The amount of the ash of the body is about 5$ of the body 

 weight, of which the skeleton furnishes over 80$ and the 



