64 THEORY AND PRACTICE 



the ends of those bronchioles become dilated and the lung is 

 emphysematous. 



When a horse with a full stomach is driven rapidly against 

 a strong wind, he is very apt to develop heaves. The pathogene- 

 sis is this : the stomach rests upon the diaphragm interfering with 

 respiration and the horse takes in too much wind and the powers 

 of expiration become tired. The horse takes in more air than 

 his lungs can dispel because the diaphragm gets tired, due to 

 pressure of the stomach. 



Nature. — Pulmonary emphysema may be either vesicular or 

 interlobular. Vesicular is seen in the horse in the form of dila- 

 tation of the vesicles. Interlobular is seen in cattle in which the 

 air is found in the interlobular connective tissue. The probable 

 reason for this difference is that in the horse there is very little 

 interlobular connective tissue and the Vv^alls of the vesicles are 

 stronger, while in cattle the interlobular connective tissue is 

 abundant and there is little or no resistance to the air passing 

 through the vesicular walls into the connective tissue around 

 them. 



Pathogenesis and Morbid Anatomy. — In this connection I 

 shall endeavor to show you the connection between cause and 

 effect and how the effect is produced by the cause through the 

 pneumogastric nerve. The pathogenesis will also include the 

 morbid anatomy. 



Assume that a horse has an excessive hereditary ap- 

 petite and is a ravenous eater; eats all that is given him, 

 wants more and is inclined to eat his bedding after he has eaten 

 his feed ! The result is distention of the stomach, partly caused 

 by eating more or less innutritions food. Over-ripe Timothy 

 hay is not fit for horse feed. If he has to eat it he should not 

 be allowed to eat more than two-thirds of the straw, this the 

 upper part; the lower third or perhaps half of it is too woody 

 and hard and contains little nourishment. Suppose now that 

 this horse with a ravenous appetite is being fed on overripe 

 Timothy hay, — he will develop the heaves. He is forced into 

 the habit of having his stomach filled with innutritions food and 

 will soon not be satisfied with the ordinary amoimt of feed. 

 The result is that the walls of the stomach become distended, 



