MECHANICAL PHENOMENA OF RESPIRATION. 311 



afterwards the ascending reaction continues more slowly; the 

 same is true with expiration, which, sudden at first, con- 

 tinues with a slow movement, lasting a considerable time 

 (Fig. 82, 3) : it may be represented in a diagram by a line 

 descending suddenly, and almost vertically, and then by a 

 very long and oblique descending line (Fig. 81 and 82). 

 Thus expiration, in short, occupies a longer time than inspira- 

 tion ; a superficial examination, however, shows only the first 

 period of expiration, which then appears extremely short, 

 shorter even than inspiration. 



The passage of the air through the respiratory tubes pro- 

 duces certain kinds of friction, and causes the inspiratory and 

 expiratory murmur (bruit) : the former sound lasts as long 

 as the action producing it ; the latter is usually perceived 

 only during the first part of this action, the current of air 



Fig. 82. Kymographic tracings of the respiration of a dog * 



being too slow and feeble in the second part, to make itself 

 heard. We see thus that auscultation of the normal respira- 

 tion would give a false idea as to the relative duration of the 

 two acts constituting respiration, by representing inspiration 

 as occupying a longer time than expiration ; what is true in 

 regard to the sounds produced not being true in regard to 

 the causes which produce them. 



Since the discovery of auscultation by Laennec many the- 

 ories have been propounded which seek to explain the sound 

 produced by normal respiration, and the changes which it 



* The double line (3) especially represents the difference between inspiration 

 and expiration. The respiration is recorded at the same moment in the trachea 

 (by variations of manometric pressure) and in the thorax (the registering drum 

 and lever being moved by the dilatations of the chest) : these two tracings are 

 contrasted for comparison. (P. Bert, "Le9ons sur la Physiologic comparee de la 

 Respiration.") 



