OUR BODIES AND HOW WE LIVE 



Experiment 55. Pass a tube through a cork ; fix the cork tightly 

 into a dry, wide-mouthed bottle. Breathe in and out of the bottle 

 several times in succession until a feeling of suffocation is felt. The 

 bottle will become moist and warm. 



If, holding the bottle upside down, we take the cork out and pass 

 a lighted splinter of wood within, the light will be at once put out, 

 for the oxygen will have almost entirely disappeared, and it is replaced, 

 by carbon dioxide. 



232. The Diffusion of Gases. Let us try to understand 

 how this exchange of gases takes place between the air 

 and the blood. 



Experiments carried on outside of the body prove that 

 gases can pass through delicate membranes. If a bladder 

 is filled with oxygen and then hung in a bottle filled with 

 carbon dioxide, the two gases will mix with each other. 

 The oxygen will pass out through the 

 thin membrane, and the carbon diox- 

 ide will pass in. This is in accordance 

 with a well-known law of physical 

 science and is known as the diffusion 



FIG. 109. Diagrammatic of S ases - 



View of an Air Sac. 233. Exchange of Gases between the 

 A, epithelial lining wall; Blood and the Air. An exchange of 



B. partition between two ,, , ,, 



adjacent sacs, in which gases really takes place in the tissues 

 run capillaries; c, fibers o f the body every moment of our 



of elastic tissue. .. 1 . . 



lives. The blood and the air cavities 



of the lungs are separated from each other only by the 

 thin and delicate epithelial lining wall of the air sacs and 

 by the walls of the capillaries. 



Blood with oxygen and carbon dioxide is on one side of 

 this thin, moist membrane, and the air in the air sacs con- 

 taining the same two gases is on the other side. The 

 proportion of carbon dioxide in the blood is greater than 



