Etiology. Pathosienesis. 225 



eign bodies (see foreign bodies in the stomach). Sometimes 

 iiniisually hirge morsels of rongli fodder may remain wedged in 

 the gullet. Sometimes also an esophageal sound which has 

 been introduced with insufficient dexterity may be swallowed 

 and may remain wedged in the gullet. Only exceptionally hair 

 balls or other foreign bodies of this kind may be displaced from 

 the rumen into the esophagus during rumination. In sheep the 

 esophagus may be obstructed by firm parts of food (beets) or 

 by large morsels. 



In horses obstruction occurs by coarse and dry feed or 

 by large morsels, if they feed greedily and do not masticate the 

 fodder properly and mix it with saliva, or when the reflex irri- 

 tability of the esophageal nerves has been diminished by a 

 previous narcosis. More rarely the esophagus of horses be- 

 comes obstructed by foreign bodies, such as eggs, pills, broken- 

 off pill sticks, sounds, swallowed milk teeth, etc. 



In swine, the affection occurs quite often and the obstruc- 

 tion is caused by pieces of potatoes, fruit, leaves, etc. 



The esophagus of dogs may l)econie ol)structed l)y parts of 

 the food (bones, cartilages, large pieces of meat or sinews, fish- 

 bones) or by foreign bodies mixed with the food, or by objects 

 swallowed in play. 



Exceptionally a foreign body that has been swallowed may 

 get into the esophagus in vomiting and may become wedged in 

 its wall (Zietschmann). 



In horses, foreign bodies are usually found in the thoracic 

 portion of the esophagus, in other animals most frequently di- 

 rectly behind the pharynx or in front of the thoracic aperture. 



Pathogenesis. When parts of the food or foreign bodies 

 become wedged in the esophagus, they usually cause a complete 

 obstruction of its lumen, in very exceptional cases a thin 

 wedged-in foreign body may cause a more or less incomplete 

 stenosis of the lumen. Total obstruction prevents deglutition 

 and the expulsion of the gastric contents (as in rumination, 

 eructation, vomiting). After partial obstruction by thin bodies, 

 fluid, gaseous, or thin mushy matters may still be transported 

 in either direction. Whenever a foreign body becomes lodged 

 in the esophagus, it causes convulsive contractions of the eso- 

 phageal muscularis and pain while the spasm lasts. The animal 

 experiments of Kahn and Meltzer have shown that the convul- 

 sive muscular contractions are the more frequent and the more 

 energetic and of longer duration, the nearer to the cardia tlie 

 obstruction is situated. In this manner lodgment of a foreign 

 body in the most caudal portion of the esophagus causes a con- 

 stant muscular spasm, while obstruction in the first portion of 

 the esophagus leads to less intense muscular contractions, or 

 they may be entirely absent, while sharp and pointed foreign 

 bodies produce continuous pains in consequence of trauma to 

 the wall. Stretching of the wall of the esophagus by the for- 



