Pneumothorax and Posture. 



5 



animal will in most instances continue to breathe well, although 

 the amount of inspired and expired air will be less than (about 

 two thirds of ) the normal. That such an animal is very sensitive 

 to the slightest influence which disturbs the breathing is shown by 

 the fact that if the animal is deeply under the anesthetic, clamping 

 the trachea for part of a minute will bring on the dyspnea ; if the 

 dog is not deeply under the anesthetic, the struggling of the 

 animal or irritation of the cornea, mucous membrane, etc., will 

 bring it on. 



While most dogs stand a small opening well, sudden heart 

 stoppage or dyspnea and death will follow in some instances. 

 The larger the opening, however, the more likely is an occurrence 

 of serious interference with respiration. In almost all of the ani- 

 mals in which the size of the opening approached to or exceeded 

 that of the diameter of the trachea, dyspnea and death followed- 

 No matter how slowly and cautiously the opening was made, 

 typical expiratory dyspnea ensued, the heart becomes irregular 

 and weak, the mediastinal septum bulged into the opening with 

 each violent expiration, and rupture of the septum and double 

 pneumothorax or sudden stoppage of the heart occurred. Nor 

 did it make any difference in what part of the chest the opening 

 was made, whether on the right or left side, near the apex or base 

 of the lung, near the sternum or vertebral column. When, how- 

 ever, the animal was operated upon while lying flat on its belly, 

 very different and gratifying results were obtained. When the 

 dog is lying on his belly, not only can a small opening be made 

 and the dog continue to breathe like a normal animal, but even a 

 very large opening (2-4 cm.) can be made, and breathing go on 

 regularly and quietly, almost if not quite like the normal. Even 

 one half of one chest wall can be removed and the animal survive. 

 Furthermore, if a dog on its back, with an opening in its chest I 

 cm. in diameter and with typical violent dyspnea due to the pneu- 

 mothorax, is turned on its belly, the breathing will often become 

 regular and quiet again, and the pressure of air breathed in and 

 out will be found to be several times as great as when the animal 

 was on its back. On the other hand, a dog on its belly with a 

 large opening in one pleural cavity and breathing quietly, can be 

 brought into a condition of grave dyspnea and asphyxia by turn- 



