246 Veterinary Medicine. 



expiration of coughing, and hindering its entrance during the 

 succeeding inspiration. The bronchia and bronchioles decrease 

 in size to near their termination, so that, as forced out in cough- 

 ing, the secretion enters the larger tube and allows the exit of 

 air, while 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 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 organi- 

 zation. 



Symptoms. As occurring congenitally 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 pathognomonic of these conditions. Again in hydrothorax 

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

 cause. Severe cases are marked by cyanosis. 



The lesions seen in atelectasis consists of 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 impossible. If it has resulted from bron- 



