CHAPTER XVI 

 FOOD 



281. Losses of the Body. One effect of respiration is to 

 reduce the weight of the body. A man gives off from 

 the lungs, in the course of twenty-four hours, about eight 

 ounces of carbon and about half a pint of water, which 

 are taken from the tissues of the body as worn-out mate- 

 rials. There are also other sources of loss to the body in 

 the processes of excretion, by which the waste or used-up 

 matter of the body is cast off. 



282. Sources of Restoration. These losses must, of 

 course, be made good, or the body will waste away. 

 Through the lungs we get oxygen only, while we need 

 hydrogen, nitrogen, carbon, and other chemical elements 

 besides, which enter into the composition of our bodies. 

 These come to us in the food which we eat, and are pre- 

 pared for use within the body by the process called 

 digestion. 



Food is that which, taken into the alimentary canal, sup- 

 plies material for the growth and repair of tissue, for the 

 generation of force, or for the regulation of force. 



283. Nutrition. Digestion is but one portion of a com- 

 plicated series of processes, called nutrition, which result 

 in the growth and repair of the constantly wasting tissues. 

 In its broad sense nutrition includes respiration, which 

 supplies the oxygen needed; digestion, or the conversion 



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