RESPIRATION 239 



Average respiratory rate at different ages: 



At one year 30 



" six years 25 



" twelve years 20 



Soon after this age, the normal proportion between the number 

 of respirations and the pulse rate, is as one to four. 



Nasal breathing is the natural method of introducing air into 

 the respiratory passages; mouth breathing is obstructed breathing 

 and unnatural. The obstruction is oftenest found in the naso- 

 pharynx, due to adenoid growths or hypertrophy of the naso- 

 pharyngeal tonsil. Enlarged tonsils obstruct the oro-pharynx; 

 a deflected septum (p. 27) or hypertrophied turbinal bone may 

 encroach upon the nasal passages. In all of these conditions 

 mouth breathing is called to the aid of defective nasal breathing. 



Nasal breathing favors the development of the air sinuses or 

 resonance chambers which communicate with the nose. (See 

 The Voice, p. 344.) 



Important note. Mouth breathing leaves the chambers undeveloped, 

 the voice has a decidedly nasal quality and, owing to the flattening of the 

 facial surface of the maxilla (because the antrum is small) the alveolar process 

 is unduly prominent. (Many bad effects of mouth breathing might be 

 cited if space and time were available.) 



The normal respiratory sound has been well compared to the 

 rustling of leaves when the gentlest of breezes is blowing through 

 them. 



The tidal volume of air is that which constitutes a respiration 

 without effort. The air which is added by an effort of inspiration 

 (or by forced inspiration) is complemental air. That which is 

 expelled by effort in addition to a normal expiration, is reserve air. 

 A certain volume always remains in the depths of the cells in order 

 to prevent their entire collapse this is called residual air; it is 

 changed gradually and constantly. 



The organs concerned in respiration must be obedient to a con- 

 trolling nerve center common to them all, in order that they may 

 act together for the one purpose. This is called the respiratory 

 center; it is situated in the brain (in the oblongata). 



