NATURAL HISTORY OF ORGANIZED BODIES. 



293 



respiration ; that virtucd vacuum, as it is called, wliicb exists in the cavit}' of 

 the pleura, and into which the air tends to precipitate itself as soon as an opening 

 is formed at any point of the thoracic structure. Now, this phenomenon can be 

 counterfeited in a very simple manner. {Fig. 1.) 



We take a bottle whose l)ottom has been removed and is replaced by a 

 stretched membrane of caoutchouc : this bottle Avill represent the thoracic cavity, 

 while the membrane corresponds to the diaphragm. In the interior of this appa- 

 ratus we place an elastic bladder of caoutchouc, which represents the lungs. The 

 neck of the bladder is luted to the neck of the bottle, so that theie shall be but 

 one orifice, that which enables the exterior air to comnuinicate with tiie interior 

 of the bladder of caoutchouc. A hole has been formed in one side of the wall of 

 the bottle, and a cord is attached to the centre of the membrane \vliich represents 

 the diaphragm, for the ptirpose of communicating to this menibrjine movements 

 Avhich imitate the diaphragmatic action in respiration. We now proceed to place 

 this apparatus in the same conditions with the thoracic cavity. We blow through 

 the throat of the bottle into the bladder, so as to distend it until it fills the cavity 

 of the bottle and expels the air contained therein. We have thus established a 

 state of things analogous to that in Avhicli the thorax is filled by the expanded 

 lungs. If we cease to blow, leaving the lateral hole free, the wind at once enters 

 with a whistling" sound through the hole in question, precisely as happens in the 

 case of an animal whose breast has been suddenly pierced. But, if we close that 

 hole after having finished the insufflation, the bladder will continue adhering to 

 the walls of the bottle, although the throat of the latter be open. To imitate the 

 movements of the diaphragm, we exert a traction on the membrane ; the bladder 

 follows all these movements just as the lungs would do, and a reciprocating motion 

 is established between the exterior and interior air, through the throat of the bottle. 

 If we desire to measure the energy with which the bladder-lung tends to collapse 

 upon itself, a manometer is fitted to the hole in the side-wall ; the mercury will 

 now be seen to be drawn towards the apparatus with a force represented by the 

 inspiration of a column of air a certain number of centimetres in height. 



A rather curious plienoraenon sometimes occurs in surgery, being a hernia of 

 the lung through a wound of the breast. This hernia might seem inexplicable, 

 in view of the tendency of the lung in such case to collapse upon itself. If wc 

 close the throat of our bottle, an act which corresponds to the occlusion of the 

 glottis in an animal and prevents the escajje of the air from the breast, the blad- 

 der will no longer have, as before, a strong tendency to retreat upon itself; for, 

 to do that, it must become empty. At this juncture let the diaphragm be 

 stretched, which will be equivalent to a strong effort at inhalation. The blad- 

 der will then be seen to fonn a hernia through the opening in the side of the 

 bottle. The explanation of this fact is quite obvious : the air, compressed in the 



