ioo Physiology. 



life, especially those who are sitting much of the time, need 

 to pay especial attention to the matter. 



The Nasal Passages. The nasal passages are fitted for 

 the introduction of the' air (i) by being narrow, but of 

 large area ; (2) by having their lining membranes richly 

 supplied with blood; (3) by the abundant secretion of 

 mucus by this membrane. The air, coming through this 

 narrow channel, is warmed, and a large part of any dust 

 it may contain is caught by the sticky mucus that covers 

 all the walls of this passage-way. 



Breathing through the Mouth. If we breathe through 

 the mouth (especially out of doors in cold weather), the 

 air may not be sufficiently warmed before entering the 

 lungs. In breathing through the mouth much more dust 

 is carried into the lungs. Then, too, the air has a drying 

 effect on the throat, whereas the mucus of the nasal pas- 

 sages will moisten the air as it enters. The ciliums, which 

 extend from most of the cells lining the air passages, are 

 constantly causing the mucus to slowly flow toward the 

 external opening, so a good share of the dust is gotten 

 rid of. A further advantage of breathing through the 

 nose is that we detect odors, and can thus judge of the 

 quality of the air. 



Deep Breathing. It is a grateful relief to the whole 

 system to stand, stretch, inhale deeply and slowly several 

 times, and to repeat this every hour or so. Every one 

 engaged in office work or studying should form this habit, 

 especially if he does not give an hour daily to exercise. 



Control of Respiration. Breathing is an involuntary 

 action. It is under the control of the nervous system, and, 

 without attention on our part, it goes on, varying in rate 

 according to the needs of the body. About every fifth 



