1884.] Origin of the Respiratory Sounds. 421 



ducting power of distended lung ; for the same reason the voice is 

 heard less plainly on the healthy side. In the living body we are 

 listening to the sounds over a distended lung in motion and permeated by 

 air-currents, and in which possibly sound is being produced. 



In order to test the conducting power of distended lung at rest, the 

 following experiment was performed. 



A pair of lungs were arranged in the artificial thorax in the way 

 described in the first experiment, and in addition a large india-rubber 

 bag filled with air was attached to the trachea by means of a tube. By 

 keeping the handle of the bellows fixed in any given position the lung 

 within the chamber could be kept for a short time at any desired 

 degree of distension, aud by pressing at intervals upon the bag, air 

 could be forced to and fro between the bag and the lung outside the 

 chamber, without distending the lung within it. When this was done 

 the sound in the outer lung was vesicular in character, that in the 

 inner non- breathing lung bronchial ; but the intensity of the sound in 

 the inner lung varied with its amount of distension, being loudest 

 when it was collapsed, and much fainter but still bronchial when it 

 was nearly fully distended. 



If, while the outer lung was being made to breathe from the bag, 

 the handle of the bellows was allowed to move, the two lungs breathed 

 together, and the sound in the inner lung at once increased, inspira- 

 tion becoming much louder than expiration, and the sound acquired 

 the vesicular character. 



This experiment proves that the glottic and bronchial murmurs^ 

 and any other sounds elsewhere produced, are heard but faintly 

 through a distended and motionless lung, and that their resultant 

 has the bronchial character, expiration being heard as plainly as 

 inspiration ; and further, that the vesicular murmur is developed 

 Uuring the distension of this lung still further by means of a current 

 of air. The only tenable explanation of these facts is that the vesicu- 

 lar murmur is produced in the lung itself; for if it be not produced 

 in the lung it must be a conducted sound, and we have just seen that, 

 expansion of the lung diminishes its conducting power ; but the 

 peculiarity of the vesicular sound is that it is heard loudest during 

 inspiration, that is to say while the lung is expanding, and by so 

 doing becoming a worse conductor of sound. The sound is loudest 

 when the conducting power of the lung is least; it cannot, there- 

 fore, be a conducted sound. 



The sound heard over the distended but motionless lung was the 

 combination of all the sounds produced in the respiratory tract greatly 

 reduced by bad conduction, and consisted of sounds produced in the 

 glottis, at the bifurcation of the trachea, and in the substance of the 

 breathing lung. 



In the present experiment the glottic sound was represented by the- 



