98 THE HUMAN BODY. 



contrary movement after an inspiration, and when expiration 

 has taken place the need of inspiration soon makes itself im- 

 periously felt. It is impossible, in fact, to retain the breath 

 except for a very short space of time, two or three minutes 

 at the longest: the most thoroughly trained divers not being 

 able to exceed this limit. 



Respiratory sounds. In a normal condition, and when 

 awake, respiration takes place without noise when the move- 

 ment is moderate; but when inspiration and expiration are 

 strong and deep, it is accompanied by a noise caused by the 

 air passing through the nasal passages or the mouth. During 

 sleep the column of air breaks against the soft palate and 

 produces snoring. Besides these sounds, which are exterior 

 to the chest, there are others produced by the passage of 

 the air through the bronchial tubes; and when the ear is 

 applied to the chest of a person in good health, a soft and 

 regular murmur is heard in rhythm with the respiration; this 

 is called the vesicular murmur. Several morbid causes 

 change the nature of this murmur, suppress it, or produce 

 others. These are so many signs which enable the physician 

 to determine the condition of the respiratory organs. 



Frequency of respiration. In an adult in a condition of 

 repose, respiration takes place about eighteen times a minute, 

 in the infant it is more frequent. As is well known, it be- 

 comes very active under the influence of bodily exertion, or 

 under excitement from any cause whether physical or moral. 

 When, on the other hand, the attention is fixed on a laborious 

 effort, the breath is held so that it very soon becomes 

 necessary to take long and deep inspirations to compensate 

 for the insufficiency of those which preceded. This result 

 of hard work or great strain of mind should be guarded 

 against in children, as their constitution suffers greatly under 

 the influence of incomplete respiration. 



Capacity of the lungs. It is estimated that the lungs of a 

 man from thirty-five to forty years old will contain about 

 225 cubic inches of air; it is less before that age, and falls to 

 a little less than 200 cubic inches at sixty years of age. The 

 capacity is smaller in women, and varies also according to 

 the individual. It is only possible to obtain approximate 



