HYGIENE AND SANITATION 165 



To summarize, the impurities of the air may come from the 

 respiration products of man and animals, by decomposition 

 of organic matter, by various offensive trades, as copper smelt- 

 ing, alkali works, smelters, and by combustion of gas, coal, 

 and artificial lights. 



Composition of Expired Air 



N O CO2 



Expired air 79.01 16.02 4.38 



RESPIRATION 



The organs of respiration in the fowl are the nasal passage, 

 larynx, trachea, lungs, and air-sacs. 



The lungs occupy the thoracic or chest cavity, pushing out 

 between the ribs, leaving only a thin muscular wall between 

 them and the skin. 



The process by which the lungs are filled with air is known 

 as inspiration. The process by which the air is forced out of 

 the lungs is called expiration. 



The fowl is provided with six air-sacs, as follows : two at the 

 anterior portion of the thorax, two at the posterior border of 

 the same, and two rather long and large sacs, called the abdom- 

 inal air-sacs, which He along . either side of the abdominal 

 cavity. These communicate with the lungs. In addition to 

 these, in the birds of flight there are air spaces in the larger 

 bones, as the femur and humerus. 



Before the air reaches the lungs it is normally warmed by 

 passing through the nasal cavities, but air may pass through 

 the mouth into the lungs; thus, in excessive body temperature 

 as in hot weather the body temperature is lowered by the bird 

 holding its wings out from the body to give a chance of greater 

 cooHng surface (the action of the atmospheric air against the 

 skin capillaries), and by opening the mouth, and by rather 

 short, quick pants, which rapidly changes the air in the lungs, 

 thus through the watery vapor and cooling the temperature is 

 lowered. In this latter process the air is not warmed by the 

 nasal passage before entering the trachea to the lungs. The 

 anterior nares are small and are immovable, hence the volume 

 of air cannot be increased through that channel. The nasal 



