CHAPTER XXV 

 FOODS: THEIR CLASSIFICATION 



What Constitutes Food. Material is taken into the Body in 

 three physical states: solid, liquid, gaseous. We have considered 

 the gaseous intake under the head of respiration, and turn now 

 to the use by the Body of solid and liquid substances. From the 

 standpoint of physiology we may include under the head of food 

 everything, either solid or liquid which is taken into the Body and 

 used there for its normal functioning. This classification includes 

 with the foods liquid substances, such as milk and water, which 

 we ordinarily classify separately as drinks. It is clear, however, 

 that from the standpoint of the Body a classification on this 

 basis, the physical nature of the substance taken, is not very 

 helpful, and we shall therefore disregard the distinction commonly 

 made between liquid and solid foods. 



The Function of Food. If we have gotten the viewpoint which 

 the earlier chapters of this book have attempted to instil, and 

 are able to look upon the Body as a piece of machinery, we appre- 

 ciate that materials must be furnished to the Body for two pur- 

 poses: (1) to supply what it needs for the liberation of energy; and 

 (2) to provide for its maintenance and repair. The first of these 

 requirements is a simple fuel demand; anything that the Body is 

 able to burn can be used if its burning or mere presence does not 

 injure the delicate machinery. The second requirement is not so 

 simple; the repair of the complex body mechanism calls for 

 particular repair materials; in the carrying on of the Body's func- 

 tions there is a continuous loss from it of substances, such as water, 

 which must be continuously replaced; moreover, we often see fit 

 to introduce substances which we think will aid the Body in carry- 

 ing out its functions, as coffee, tea, spices, and condiments. 



Classes of Foods. We would naturally, on the basis of the 

 discussion in the last paragraph, divide all foods into two groups, 

 energy -yielding foods, and repair and maintenance foods. While 

 we shall use this classification in the main in our discussion of 



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