Atelectasis. Collapse of Lung. 207 



tion of coughing, and hindering its entrance during the succeed- 

 ing inspiration. The bronchia and bronchioles decrease in size to 

 near their termination, so that, as forced out in coughing, the se- 

 cretion enters the larger tube and allows the exit of air, which as 

 drawn back in inspiration it enters the smaller tube and closes it 

 against any possible serial entrance. Mendelssohn and Traube 

 demonstrated this action by introducing a shot into a dog's lung, 

 and in two days the left lung was found collapsed and the right . 

 one the seat of complementary emphysema. The violence and 

 frequency of the cough therefore bears a ratio to the occurrence 

 and extent of atelectasis. Other causes are the compression of 

 the lower lobes of the lung by hydrothorax, by pneumothorax 

 (developed by lacerated lung or perforated chest wall) or by a 

 false membrane contracting in process of organization. 



Symptoms. As a congenital condition in the improved meat 

 producing animals the condition is rarely recognized in life and 

 cannot be said to be a defect. The collapsed lobule being farther 

 removed from the air may be a more favorable field for the growth 

 of pathogenic bacteria, but on the other hand these do not so 

 readily penetrate it as if the tubes were open. When the collapse 

 is more extensive, the contrast in the flatness on percussion and 

 indistinctness of the respiratory murmur on the affected side, and 

 the marked resonance and loud murmur on the other, may serve 

 to identify the affection. In extensive, traumatic cases this con- 

 trast is much more prominently marked, as the expanded portions 

 have to take on extra compensatory work and are not infrequently 

 rendered emphysematous. The drum-like sound in percussion of 

 such parts, and in the upper part of the chest in pneumothorax 

 are pathognomomic of these conditions. Again in hydrothorax 

 the horizontal upper level of the area of dulness betrays a liquid 

 cause. Severe cases are marked by cyamosis. 



The lesions seen in atelectasis consist in depressed areas of a 

 dark fleshy color on the surface of the lung, usually sharply lim- 

 ited by the borders of the lobules, and in strong contrast with the 

 bulging, light colored lobules adjacent, which are often emphy- 

 sematous. The collapsed lobule may usually be dilated when air 

 is forced into the bronchium, but if it has been of some standing 

 this is often difficult or impo-ssible. If it has resulted from bron- 

 chitis or compression of a previously inflated lung it will often 



