128 RESPIRATION RESPIEATORY MOVEMENTS. 



26, at the age of five years ; 



20, between fifteen and twenty years ; 



19, between twenty and twenty-five years ; 



16, about the thirtieth year ; 



18, between thirty and fifty years. 



The influence of sex is not marked in very young children. There is no 

 difference between males and females at birth ; but in young women, the 

 respirations are a little less frequent than in young men of the same age. 



The various physiological conditions which have been noted as affecting 

 the pulse have a corresponding influence on respiration. In sleep the num- 

 ber of respiratory acts is diminished by about twenty per cent. (Quetelet). 

 Muscular effort accelerates the respiratory movements pari passu with the 

 movements of the heart. 



Relations of Inspiration and Expiration to each other Respiratory 

 Sounds. In ordinary respiration, inspiration is produced by the action of 

 muscles, and expiration, by the passive reaction of the lungs and of the elas- 

 tic walls of the thorax. The inspiratory and expiratory acts do not immedi- 

 ately follow each other. Beginning with inspiration, it is found that this 

 act maintains about the same intensity throughout. There is then a very 

 brief interval, when expiration follows, which has its maximum of intensity 

 at the beginning of the act and gradually dies away. Between the acts of 

 expiration and inspiration is an interval, which is somewhat longer than the 

 interval between inspiration and expiration. 



The duration of expiration is generally somewhat longer than that of 

 inspiration, although the two acts may be nearly, or in some instances, quite 

 equal. After five to eight ordinary respiratory acts, an effort generally occurs 

 which is rather more profound than usual, by which the air in the lungs is 

 more thoroughly changed. The temporary arrest of the acts of respiration 

 in violent muscular efforts, in straining, in parturition etc., is sufficiently 

 familiar. 



Ordinarily respiration is not accompanied by any sound which can be 

 heard without applying the ear directly, or by the intervention of a stetho- 

 scope, to the chest, except when the mouth is closed and breathing is carried 

 on exclusively through the nasal passages, when a soft, breezy sound accom- 

 panies both acts. If the mouth be opened sufficiently to admit the free pas- 

 sage of air, no sound is to be heard in health. In sleep the respirations are 

 more profound ; and if ' the mouth be closed the sound is rather more 

 intense. 



Snoring, which sometimes accompanies the respiratory acts during sleep, 

 occurs when the air passes through both the mouth and the nose. It is more 

 marked in inspiration, sometimes accompanying both acts, and sometimes it 

 is not heard in expiration. It is not necessary to describe the characters 

 of a sound so familiar. Snoring is an idiosyncrasy in many individuals, 

 although those who do not snore habitually may do so when the system is 

 unusually exhausted and relaxed. It occurs only when the mouth is open, 

 and the sound is produced by vibration and a sort of flapping of the velum 



