1884.] Origin of the Respiratory Sounds. 419 



the respiratory tract. The cross section of the respiratory tract 

 increases from the trachea to the vesicles, just as the cross section of 

 the circulatory system increases from, the aorta to the capillaries, and 

 the rate of the air-current varies accordingly. When a larger or 

 smaller bronchus is obstructed the cross sections of the bronchi and 

 vesicles are more or less diminished, and the rate of the air-current 

 in them proportionately increased, the rate in the trachea being 

 unaffected by the obstruction as such. 



And, secondly, that when a bronchus is obstructed a sound is pro- 

 duced by the air passing over its mouth. 



The diminution in the time occupied in inspiration and expiration, 

 brought about by the obstruction of a bronchus, is probably one cause 

 of the increased frequency of respiration in cases where the lung is 

 consolidated or compressed. 



With regard to the theory of the laryngeal production of bronchial 

 breathing, it is to be observed that in a case of complete consolida- 

 tion of one lung each respiratory act must be performed in less than 

 half the normal time before any increase in the rate of the air-current 

 in the larynx and trachea, and therefore of the sound produced in 

 them, can occur. 



Repeating the above experiment with calves' lungs, the same result 

 was obtained. Both lungs were placed in the artificial thorax with 

 the trachea and main bronchi above the cover. On compressing 

 either of the bronchi a marked increase of sound was heard over the 

 trachea, the increase in the expiratory sound being as before the 

 greatest. The shortness of the main bronchi made it impossible to 

 elicit different notes by compressing them at different points ; but it is 

 probable that a partial consolidation by obstructing the smaller tubes 

 ^ would produce a different note from that obtained by stopping the air- 

 current in the main bronchus. 



The explanation of the fact that the expiratory is increased more 

 than the inspiratory sound appears to be the following : 



During both inspiration and expiration a sound is produced by the 

 passage of the air over the mouth of the obstructed tube. During 

 inspiration this is the only new sound produced, the air passing from 

 the trachea to the bronchus, that is, from a larger to a smaller tube, 

 as shown in fig. 6, but during expiration the air passes from the 

 bronchus to the trachea from a smaller to a larger tube which, as 

 is well known, is a sufficient cause to produce a sound. Therefore 

 during inspiration a cause for the production of one, and during 

 expiration causes for the production of two new sounds are present. 



The passage of the air from the two smaller tubes into the larger 

 ones does not produce any considerable sound, for when they are 

 both open the expiratory and inspiratory sounds are much alike. 



It appears to me that in these experiments the conditions present 



