BREATHING.] PHYSIOLOGY, 85 



through the blood the body, is nourished. These are 

 food and air. The air we have always with us, we 

 have no need to buy it or toil for it \ hence we take it 

 as we want it, a little at a time, and often. We gather 

 up no store of it ; and cannot bear the lack of it for 

 more than a few moments. . \ . . ,.v 



For our food we have to labour ; we store it up in 

 our bodies from time to time, at intervals of hours, 

 in what we call meals, and can go hours or even days 

 without a fresh supply. 



Let us first of all see how the blood, and, through 

 the blood, the body, is nourished by air. 



HOW THE BLOOD IS CHANGED BY AIR : 

 BREATHING. § VI. 



36. I have already said, perhaps more than once, that 

 our muscles burn, burn in a wet way without giving 

 light. And when I say our muscles, I might say our 

 whole body, some parts burning more fiercely than 

 others. , 



You have learnt from your Chemistry Primer (Art. 

 2, p. 2) what happens when a candle is placed in a 

 closed jar of pure air. The oxygen gets less, carbonic 

 acid comes in its place, and after a while the candle 

 goes out for want of oxygen to carry on that oxida- 

 tion which is the essence of burning. You also 

 know that exactly the same thing would happen if 

 you were (only you need not do it) to put a bird or a 

 mouse in the jar instead of a candle. The oxygen 

 would* go, carbonic acid would come, and the little 

 flame of hfe in the mouse would flicker and go out, 

 and after a while its body would be cold. 



But suppose you were to nut a fish or a snail in a 



