148 ALIMENTATION 



greater or less quantity. The same is true of vegetable products. All 

 the organic nitrogenous matters contain mineral substances which can 

 not be separated without incineration. When new organic matter is 

 appropriated by the tissues to supply the place of that which has 

 become effete, mineral substances are deposited with them ; and the 

 organic matters, as they are transformed into excrementitious sub- 

 stances and discharged from the body, are always thrown off in con- 

 nection with the mineral substances with which they are associated. 

 This constant discharge of inorganic matters, forming, as they do, an 

 essential part of the organism, necessitates their introduction with the 

 food in order to maintain the normal constitution of the parts. As 

 these matters are necessary to the proper constitution of the body, 

 they must be regarded as alimentary substances. 



Water. This is one of the most important of the constituents of 

 the organism, is found in every tissue and part without exception, is 

 introduced with all kinds of food and is the basis of all drinks. As a 

 rule it is taken in greater or less quantity in a nearly pure state. 

 Although, as a drink, water should be colorless, odorless and tasteless, 

 it always contains more or less saline and other matters in solution, with 

 a certain quantity of air. The air and gases may be driven off by 

 boiling or by reducing the atmospheric pressure. The demand on the 

 part of the system for water is regulated to a certain extent by the 

 quantity discharged from the organism, and this is subject to great 

 variations. The quantity taken as drink also depends on the constitu- 

 tion of the food as regards the water that enters into its composition. 



Water is beyond comparison the most important compound in 

 Nature. It is essential to all chemical changes that occur out of the 

 body and to all processes of digestion, anabolism and katabolism. It 

 is the most powerful dissocient known. According to modern views, 

 molecules have no chemical activity and chemical combinations occur 

 only when they are dissociated into ions. Anhydrous hydrochloric acid 

 will not decompose carbonates ; pure sulphuric acid has no action on 

 dry litmus ; dried ammonia and hydrochloric acid will not combine if 

 brought together; and other illustrations might be given of the action 

 of water in chemical combinations. 1 



Although organic compounds dissociate into ions slowly and feebly, 

 water is the most important agent in their chemical changes. The 

 subject, however, of the possible and probable reactions between pro- 

 teids and water is so vast, and as yet the results of experiments have 



1 According to Dewar, a chemical combination can occur, in the absence of water, at very 

 low temperatures, such as that of liquid air ; but at present, this is the only exception to the 

 general proposition stated above. 



