CHAPTER II 



DIGESTION 



14. Digestion. We have seen how the little amebas can 

 take food into any part of their bodies, and then can change 

 it so that it becomes a living part of themselves. Each 

 ameba has to seek its own food, and to take it just as it 

 is found. The cells of our bodies have their food pre- 

 pared for use and brought to them by a few of the cells 

 of the body set aside for that special work. This food is 

 the blood. All food eaten must become a part of the blood 

 before it can nourish the body. 



The preparation of food so that the cells can use it is f 

 called digestion. The object of digestion is to separate 

 food from its hard and waste parts, and then to soften 

 and dissolve it so that it becomes a liquid and can flow 

 with the blood. 



15. Cooking. Man usually begins digestion outside of 

 his body by cutting his food into pieces and heating or 

 cooking it. By cooking most kinds of albumin are changed 

 to a jelly like or solid form, like a cooked egg, but some 

 kinds, like the connective tissue which binds the cells to- 

 gether, are softened. Cooking should leave food so soft 

 that it can be chewed easily. Usually the longer food is 

 cooked, the softer it becomes. 



Cooking softens starch grains and causes them to swell 

 and burst, and finally to dissolve in water, forming a thin 

 paste. Man cannot digest raw starch, and so it must be 



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