CHAPTER XX 



THE CHEMICAL BASIS OF THE BODY* 



A large number of elements enter into the composition of the 

 body — oxygen, hydrogen, carbon, nitrogen, sulphur, phos- 

 phorus, chlorine, iodine, fluorine, silicon, potassium, sodium, 

 calcium, magnesium, and iron. Only to a very limited extent 

 are these found free in the body. They are generally brought 

 together in such a way as to form compounds, and these are 

 divided into two main groups — organic and inorganic. 



The organic group consists of protein, a little carbohydrate, 

 and fat. The same substances are found in plants, though not 

 in the same proportion. In the great cycle of events in the 

 universe, nothing is lost — plants build, animals destroy. The 

 products of destruction find their way back to the earth to be 

 utilised by plants, and once more served up for the use of animals. 

 Plant life is synthetic, and the chemical processes are mainly 

 those of reduction ; animal life is analytic, and the chemical 

 processes mainly those of oxidation. The plant converts 

 kinetic into potential energy, while in animals the reverse 

 process occurs, and the potential energy contained in food is 

 converted into kinetic. A simple, though vast, cycle of reciprocal 

 events is occurring between vegetable and animal life. 



The common platform on which these meet is the cell, which 

 has been briefly considered at p. 698. The structure, chemistry, 

 and physics of the cell is the same everywhere. Widely as cells 

 may differ in shape, they conform to a common structural and 

 functional plan in plants and animals, the essential feature being 

 the protoplasm for nutrition and the nucleus for reproduction. 

 Of the highly complex protoplasm but little is known. It 

 behaves as living material in that it requires food and oxygen ; 

 it digests and excretes ; it moves, behaves as if it had sensation, 

 reproduces itself, and finally becomes worn out and dies. Of 



* It is not intended in this chapter to do more than to elucidate and 

 supplement some of the chemical statements scattered throughout the 

 previous chapters. 



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