FOOD 195 



and carbonates of lime from wheat and other grains ; 

 sulphur is contained in eggs ; iron is contained in grains, 

 tomatoes, and most vegetables. Iron tonics, tincture of 

 iron, etc., do not contain iron in an organic form. Only 

 plants can furnish these mineral foods in a form most 

 suitable for assimilation by our bodies. Animals must 

 get them from vegetables, and they may become part of 

 the bodies of several successive animals as one makes food 

 of another. 



335. But you may ask, how is it that plants only have 

 the power of nourishing themselves with mineral sub- 

 stances although we take water and common salt as food? 

 Are these two exceptions to the rule ? It is doubtful whether 

 such substances can be strictly called foods, for food must 

 undergo a chemical change in the body, while water and 

 salt do not, but are found to leave the body unchanged 

 in the perspiration and other excretions. They serve only 

 a mechanical purpose of dissolving the true foods and 

 bringing them within the reach of the cells, for it was 

 learned that all the cells lead a watery existence. Nerve 

 cells, as well as others, are bathed in lymph, and it is in 

 a manner true that we even think under water. The 

 mechanical foods, are therefore of the greatest importance in 

 keeping the tissues in the right condition for the cells to 

 work. 



336. Table: 



FOOD STUFFS 



f Proteids Nitrogenous substances. 

 Organic \ Fats and oils 1 Non-nitrogenous 



[ Sugars and starches J substances. 



\. Inorganic ! Waten 



I Salts (salines). 



The non-nitrogenous foods are sometimes called carbo- 

 naceous foods because they contain a greater amount of 

 carbon than the proteids ; remember, however, that the 

 proteids have some carbon. 



