On Respiration 187 



suppose that a bladder is enclosed in the cavity of a 

 pair of bellows, and that its neck is so fixed to the 

 pipe of the bellows which is placed in it, that air 

 blown into the pipe can pass only into the bladder, as 

 is seen in Plate II., Fig. 6. (But to ensure this result^ 

 the bladder should be fitted in that manner to the 

 pipe before the latter is attached to the bellows.) 

 Further, let the hole be made not as is usual in the 

 lower blade of the bellows, but in the upper one, and let 

 it be of considerable size. Let it also be perfectly closed 

 by a plate of glass, attached to the blade by a suitable 

 cement, so that the bladder shut up within may be seen 

 through the glass as through a window. When these 

 preparations have been made, you will see, if the 

 bellows are opened by drawing the blades apart, the 

 bladder swell and extend into the enlarged cavity of 

 the bellows, as is shown in the figure referred to. 

 And indeed it is plainly in the same way that the 

 inflation of the lungs in the dilated chest is produced. 

 From this we conclude that the lungs are distended 

 by the air rushing in, and that they do not expand of 

 themselves, as some have supposed ; for the nmscles^ 

 and fibres which are requisite for any motion are 

 absent in the lungs. And indeed although the lungs 

 were provided with muscles, under their contractile 

 action the lungs would not expand but rather con- 

 tract, as happens to the bladder and stomach, and 

 other organs of the kind. And further, when the 

 thorax is pierced, the lungs in)mediately collapse at 

 that place — a clear proof certainly that their move- 

 ment is not spontaneous, but depends entirely on that 

 of the chest. As for the nerves which are distributed 

 in the trachea and bronchia, they do not serve for 

 movement, but for sensation and the nutrition of 

 these organs. 



