418 Mr. J. F. Bullar. Experiments to Determine the [Nov. 27, 



respirations were performed, and by working with a proper force the 

 sound could be made very faint indeed. If, when this was the case, 

 one of the smaller tubes was nipped, so as to prevent any air passing 

 through it, while continuing to work the bellows with the same force, 

 the sounds became greatly increased. 



The expiratory sound was increased more than the inspiratory, and 

 at the same time the character of the sound changed, a note could be 

 detected in it whose pitch varied with the part of the tube pinched, 

 the shorter the length of tube between the bifurcation and obstruc- 

 tion the higher being the pitch. 



The sounds could be heard either at the mouth of the large tube 

 (trachea) or with the stethoscope in the obstructed and unobstructed 

 tubes (bronchi). 



In this experiment if the bellows be worked at a uniform rate, the 

 rate of the air-current in the large tube will not be appreciably 

 affected by the stoppage of one of the smaller tubes. (If altered it 

 will be diminished on account of the slight increase of friction.) 

 The rate of the air-current through the trachea being unchanged 

 by the stoppage of a bronchus, the increase of sound cannot be 

 produced in the glottis. We must seek therefore in some part of 

 the respiratory tract below the trachea for the origin of the sound 

 caused by bronchial obstruction. The stoppage of one bronchus, 

 although not affecting the rate of the air-current in the trachea, 

 doubles its rate in the free bronchus, for when one bronchus is 

 shut all the air entering the trachea passes through the free bronchu.8, 

 and fills the bag (lung) belonging to it in the same time in which 

 the two bags would have been half-filled had both the bronchi 

 been free. The stoppage of one bronchus not only increases the rate 

 of the air-current in the other, but produces conditions for the 

 development of a new sound at the bifurcation of the trachea, for as 

 the air passes along the free bronchus it blows across the mouth of 

 the obstructed tube, and a current of air crossing the mouth of a 

 tube produces a sound. A sound produced in this way, like the sound 

 in the experimeut, varies according to the length of the tube blown 

 across, a rushing noise is produced at the mouth of the tube, and the 

 tube, according to its length, brings into prominence some particular 

 note present in the noise, and so modifies its character. 



By working the bellows so as to completely fill and empty the 

 bags at each stroke, the same amount of air is made to pass through 

 each small tube, whether the other be shut or open, but when one 

 tube is shut the whole act of inspiration or expiration comes to an end 

 in half the time occupied when both the tubes are open. 



The important points to remember are 



First, that the obstruction of a bronchus upsets the ratio normally 

 existing between the rates of the air-current in the different parts of 



