SUMMARY.] PHYSIOLOGY. . 127 



THE WHOLE STORY SHORTLY TOLD. § IX. 



55. And now you ought to be able to understand 

 how it is that we live on the food we eat. 



Food, inasmuch as it can be burnt, is a source of 

 power. In burning it gives forth heat, and heat is 

 power. If we so pleased, we might burn in a furnace 

 the things which we eat as food, and with them drive 

 a locomotive or work a mill ; if we so pleased, wc 

 might convert them into gunpowder, and with them 

 fire cannon or blast rocks. Instead of doing so, we 

 burn them in our own bodies, and use their power in 

 ourselves. 



Food passing into the alimentary canal is there 

 digested ; the nourishing food-stuffs are with very little 

 change dissolved out from the innutritions refuse ; 

 they pass into and become part and parcel of the 

 blood. 



The blood, driven by the unresting stroke of the 

 heart's pump, courses throughout the whole body, and 

 in the narrow capillar! is bathes every smallest bit of 

 almost every part. Kept continually rich in combus- 

 tible material by frequent supplies of food, the blood 

 as well at every round sucks up oxygen from the air 

 of the lungs ; and thus arterial blood is ever carrying 

 to all parts of the body, to muscle, brain, bone, nerve, 

 skin, and gland, stufif to burn and oxygen to burn it 

 with. 



Everywhere oxidation, burning, is going on, in some 

 spots or at some times fiercely, in other spots or at 

 other times faintly, changing the arterial blood rich in 

 oxygen to venous blood poor in oxygen. From most 

 places where oxidation is going on, the venous blood 



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