FOOD 209 



the muscular tissue is rapidly broken down under the 

 strong contraction constantly called for, and the circula- 

 tion becomes swifter to supply material to rebuild the 

 decomposed cells. Respiration, too, must be quickened 

 to furnish a sufficient quantity of oxygen to arterialize 

 the blood flowing faster to the lungs, loaded with the 

 products of chemical changes in the tissue cells. Nerv- 

 ous tissue also is worn away by the constant demands 

 upon it for conveying impulses to the many muscles 

 engaged and in coordinating all their related actions. 



If the body is exposed to a low temperature, a still 

 larger demand is made for food to supply the greater loss 

 of heat. During the period of growth a quantity of food 

 is needed in excess of the waste products to furnish mate- 

 rial for enlarging and strengthening all parts of the 

 body. 



299. Undigested Food. Some (an average of about one 

 tenth) of the food taken into the stomach, and especially 

 a part of our vegetable food, seems to play no part in sup- 

 plying nutrient material, but passes through the alimen- 

 tary canal to be expelled from the body unchanged. It 

 serves, however, as an aid to digestion by giving an 

 increase of bulk to the food, and so assists the action of 

 the digestive organs. 



300. Cooking is the application of heat in one way or 

 another to articles used as food. Most of our diet comes 

 to the table after being submitted to this process, which 

 renders it more wholesome and more palatable. By cook- 

 ing, which lessens the cohesion of particles, the amount 

 of work required of the digestive organs is reduced, and 

 the chemical effects of heat prepare the various elements 

 in the food to receive more readily the action of the diges- 

 tive juices. Cooking also develops, especially in animal 



