PART I. 



THE FOODS 



CHAPTER I. 

 THE SIGNIFICANCE OF FOODSTUFFS. 



THE CHEMICAL RELATIONSHIP OF ANIMALS AND PLANTS. 



In considering the nature of the foods and their elaboration into 

 living matter, it is necessary in the first place to realize that the foods 

 of multicellular animals such as ourselves, are, at the same time, the 

 constituents out of which living matter is built up. This becomes 

 evident when we recollect that the majority of our foodstuffs consists 

 of matter that was formerly living or which is derived from matter 

 that was formerly living. Meats and vegetables and grains are, of 

 course, matter that w r as awhile ago alive, that is now arrested in its 

 function and more or less rapidly decomposing into more elementary 

 substances, but still contains, for the most part, the components of 

 living protoplasm. Perhaps they are not linked together in precisely 

 the way in which they are linked together in truly living matter, and 

 perhaps the fact that this matter is no longer living is attributable to 

 this disturbance in the linkage of its constituents. Still the con- 

 stituents are there, and we appropriate them, modify them in some 

 degree, and build them up into our own tissues. Other foodstuffs, 

 such as sugar, are directly extracted from living tissues in which they 

 form stores or reserves of energy, for example from beets or sugar-canes, 

 and these are likewise appropriated to our own use. 



In this respect we differ very materially from the plants, the foods 

 of which are in general very much more elementary than ours. Plants 

 are actually able to build up living tissues out of substances which have 

 in themselves no necessary connection with living protoplasm; out of 

 mineral salts, water and carbon dioxide. For this reason it used to be 

 thought that only plants possessed the pow r er of synthesizing the actual 

 constituents of living matter and that we, without doing any fresh 

 construction, simply sort out and appropriate these preformed con- 

 stituents and thus live in a state of parasitism upon the vegetable 

 world. 



