THE RESPIRATION 



iniquity to any but a person densely ignorant of hygiene. 

 Heating by fireplaces (Fig. 82) is the most healthful of 

 all methods, for there is a constant removal of air through 

 the chimney, and this air will be replaced ; even if all 

 doors and windows are closed, it will come in through tiny 

 cracks. Radiant heat travels in straight lines from a 

 fireplace and warms solid objects, but not the air passed 

 through. Hence an open fire will keep the body warm 

 with the room at a low temperature. Fireplaces, however, 

 do not afford sufficient heat in severe climates. 



Stoves are not as healthful as fireplaces, for there is not 

 so much air removed through 

 the pipe as through the 

 chimney. Carbon monoxid, 

 unlike carbon dioxid, is an ac- 

 tive poison causing the blood 

 corpuscles to shrivel. It 

 passes through red-hot iron 

 or a cracked stove or furnace. 



FIG. 83. BLACKBOARD SKETCH. 



Reasons for Breathing through the 

 Nose (Fig. 83). (i) The many 

 blood vessels in the mucuous mem- 

 brane lining the nasal passages so 

 heat the air that it does not irritate the bronchial tubes. (2) The hairs 



in the nostrils strain the air and catch 

 dust ; the cilia of the nasal passages 

 also do this. (3) A mouth-breather 

 often swallows food before chewing it 

 sufficiently, because he cannot hold his 

 breath longer. (4) The nasal mucous 

 membrane of an habitual mouth- 

 breather dries and shrinks and ob- 

 structs the circulation, bringing on 

 catarrh of the nose. (5) Mouth breath- 

 ing causes an unpleasant expression of 

 countenance (see Fig. 84). (6) The 



FIG. 84. Facial expression in 

 mouth breathing, and breath- 

 ing through the nose. 



