1 04 Physiology. 



the tissues of the body. Oxygen unites with this carbon, forming car- 

 bon dioxid. We know that there is carbon in beef, for when it is over- 

 baked we see 'the black carbon where it is charred. There is carbon in 

 our muscles and in all the other tissues. 



EXPERIMENT 5. Place a nail, or any piece of iron, in a tumbler of 

 water. It will soon rust. Rusting is caused by the union of oxygen 

 with the iron. When anything unites with oxygen it is said to oxidize. 

 When the union is rapid, as with the burning candle, it is called com- 

 bustion. 



EXPERIMENT 6. Hold a thermometer at arm's length. It shows 

 the temperature of the air, of the air you are breathing in. Breathe 

 for a few minutes upon the bulb of the thermometer and you have proof 

 that the air we breathe out is warmer than the air we breathe in. 



How the Body is like a Candle. The burning candle 

 and the body both produce heat. To do this each must 

 have oxygen. The oxygen unites with carbon and other 

 elements in each, and produces carbon dioxid, water, and 

 other substances. And just as a candle flame is soon put 

 out in a closed tumbler, so life would be destroyed by suf- 

 focation if an animal were shut in an air-tight room. 



Exchanges between the Air and the Blood in the Lungs. 

 Whatever the air coming from the lungs contains that was 

 not in the air entering them it has taken from the blood, 

 and what the air has lost it has given to the blood. The 

 air in the air vesicle is separated from the blood in the 

 pulmonary capillaries only by the thin wall of the air vesicle 

 and the thin capillary wall. 



What the Air gets from the Blood. Carbon dioxid, water, 

 and other waste matters pass from the blood through this 

 thin partition into the air vesicle, to be sent out by later 

 expiration through the bronchial tubes and windpipe. The 

 air also gets heat from the blood (see Fig. 60). 



