NON-OXIDIZABLE FOODS. 29T 



is insoluble in pure water, but dissolves readily if a small 

 quantity of neutral salts is present. Besides such uses the 

 non-oxidizable foods have probably others, in what we may 

 call machinery formation. In the salts which give their 

 hardness to the bones and teeth, we have an example of 

 such an employment of them: and to a less extent the 

 same may be true of other tissues. The Body, in fact, is 

 not a mere store of potential energy but something more 

 it is a machine for the disposal of it in certain ways; and, 

 wherever practicable, it is clearly advantageous to have the 

 purely energy-expending parts made of non-oxidizable mat- 

 ters, and so protected from* change and the necessity of 

 frequent renewal. The Body is a self -building and self- 

 repairing machine, and the material for this building and 

 repair must be supplied in the food, as well as the fuels, or 

 oxidizable foods, which yield the energy the machine ex- 

 pends; and while experience shows us, that even for ma- 

 chinery construction, oxidizable matters are largely needed, 

 it is nevertheless a gain to replace them by non-oxidizable 

 substances when possible; just as if practicable it would be 

 advantageous to construct an engine out of materials which 

 would not rust, although other conditions determine the 

 use of iron for the greater part of it. 



Definition of Poods. Foods may be defined as sub- 

 stances which, when taken into the alimentary canal, are- 

 absorbed from it, and then serve either to simply material 

 for the growth of the Body, or for the replacement of matter 

 which has been removed from it, either after oxidation or 

 without having been oxidized. Foods to replace matters 

 which have been oxidized must be themselves oxidizable; 

 they are force generators, but maybe and generally are also 

 tissue formers; and are nearly always complex organic sub- 

 stances derived from other animals or from plants. Foods 

 to replace matters not oxidized in the Body axe force regu- 

 lators, and are for the most part tolerably simple inorganic 

 compounds. Among the force regulators we must, how- 

 ever, include certain organic foods which, although oxidized 

 in the Body and serving as liberators of energy, yet produce 

 effects totally disproportionate to the energy they set free. 



