362 ELEMENTS OF GENERAL SCIENCE 



more air in the lungs. It is the demand for oxygen in the 

 tissues which stimulates an increase in the rate of breathing. 

 Any boy or girl who has run until exhausted knows that 

 at such a time the body needs more air than usual. If a 

 mouse or other animal is placed under a bell jar and the air 

 is exhausted, the animal breathes rapidly and with the same 

 violent efforts to get air that are shown by an animal that 

 is exhausted from exercise. 



Any exercise that tends to increase the air capacity of the 

 lungs increases one's ability to supply his blood with oxygen 

 and to remove waste products from the blood. Deep-breath- 

 ing exercises are of great importance in increasing the lung 

 capacity. Vigorous exercise is helpful to many persons, since 

 such exercise often compels them to breathe deeply a tiling 

 which they should practice whether compelled to or not. 



It needs no argument to show that pure air is better for 

 the body than impure air. The nasal passages are so con- 

 structed as to assist in screening out floating particles, as bac- 

 teria and dust. Persons who breathe through the mouth are 

 likely to accumulate dust in the passages leading to the 

 lungs, and in large cities with dusty air such persons may 

 accumulate enough dust to prove a menace to the work 

 of the lungs. Collections of dust may become sources of 

 irritation and may be the starting points for the growth 

 of disease germs, such as those of tuberculosis. Air that is 

 breathed inward through the nose in winter time is warmed 

 before entering the lungs, but if taken in through the mouth 

 its temperature is changed but little before reaching the 

 lungs and may chill the lung tissue. " Mouth breathers " 

 should consult a physician to determine whether there is any 

 structural reason for their practice. If not, careful attention 

 will enable them to change the habit to normal breathing. 



