THE RESPIRATORY ORGANS 



173 



which takes place in the burning or oxidizing of fuel in a stove. 

 If all air (oxygen) were kept from entering the blood, i.e. if 

 the dampers were shut, the foods, even though digested and 

 in the blood, could not be oxidized, and would be only so much 

 dead weight and of no value. The stove is connected with a 

 chimney to carry off the smoke and other gases that are 

 formed in the burning fuel. Gases are also formed in the body 

 by the oxidizing of foods, and these likewise must be passed off. 

 The body needs to exchange gases with the air. Respiration 

 is the process of gas exchange in the tissues of living things. 



THE NOSE AND PHARYNX 



Figure 40 shows the structure of the nasal passages. Air 

 enters by the two nostrils into the nasal chambers, or canals 

 which are separated from one another by a partition made of 

 cartilage and connective tissue in front, and strengthened 

 farther back by a thin vertical sheet of bone. The canals 

 pass back through the nose, just above the hard palate, and 

 enter the upper por- 



drain, 



'Olfactory 



Nerve 



tion of the pharynx 

 by separate openings. 

 The bony and car- 

 tilaginous partition 

 between the two nasal 

 canals presents a fairly 

 smooth surface; but 

 the opposite wall of 

 each canal has, pro- 

 jecting into it, a much 

 folded, wrinkled, 

 spongy arrangement 

 of thin bones, the tur- 

 binated bones; Fig. 96. 

 The walls of the nose cavities are covered with a smooth 

 epithelium which contains innumerable mucous gland cells. 



FIG. 96. VERTICAL SECTION THROUGH THE 



NOSE 



Showing the turbinated bones and the olfactory 

 nerve entering from the brain into the upper nagal 

 passages. 



