OF VETERINARY MEDICINE. 63 



Hydrocyanic acid is recommended by some text-books, but 

 I have not had success with it. It kills by paralyzing the heart. 



HEAVES OR PULMONARY EMPHYSEMA. 



This disease is known among horsemen as broken zuiiid. 

 Pulmonary emphysema would seem a paradoxical expression be- 

 cause emphysema indicates that air is present where it should 

 not be : but in this case we have dilated air vesicles and an ex- 

 cess of air in a place where air is normally present. 



Nature. — Pulmonary Emphysema is a neurosis affecting the 

 pneumogastric nerve, and incidentally the heart and lungs. In 

 the lungs the air vesicles dilate and sometimes rupture, with ex- 

 tensive destruction of the contractility of the lung substance. 

 Consequently dyspnoea results. 



Etiology. — We divide the causes into four classes: 1. 

 Heredity; 2. Breed; 3. Dietetics; 4. Structural changes, de- 

 pendent upon a previously diseased condition. 



It is not difficult to say wherein heredity produces heaves — 

 so much so that in localities where stallion inspection is practiced, 

 a "heavy" stallion cannot stand in a public stud, and this is 

 proper. Heaves is unquestionably hereditary. Dr. Baker sug- 

 gests that this factor may have a relation to the gluttonous appe- 

 tite of the parent. 



Breed is not a very important factor in the etiology. Prof. 

 Robertson claimed, however, that the light draft breed is most 

 subject to heaves. 



Dietetics cuts a very important figure. This even plays its 

 part in heredity. A bulky innutritions diet, tends tO' produce 

 heaves — especially is overripe Timothy hay a very common cause 

 of heaves. All horses living on overripe Timothy do not have 

 heaves, but heredity comes in to determine the percentage. 



In structural changes depending upon a previously diseased 

 condition, the lungs may have had their function partially sus- 

 pended by pneumonia or bronchitis and the healthy part had to 

 do the work of the whole, in which a chronic dilatation of the 

 air vesicles took place in the healthy part. 



In case of dilatation of the bronchioles, the air vesicles at 



