Hereditary Diseases of Horses. 



117 



Chronic Cough depends on excessive irritability of the mucous 

 membrane of the trachea or bronchii, and often occurs as a 

 consequence of bronchitis. In unfavourable states of the atmo- 

 sphere it is greatly aggravated, and in all such cases the slightest 

 over-exertion is sufficient to cause a painful, harassing cough. 

 This irritable condition is very apt to be hereditary. A thick- 

 ened state of the same mucous membrane, inducing thick wind, 

 grunting, and some of the cases considered as broken wind, is 

 also hereditary ; and the same obtains with roaring^ especially 

 that form of it which alone, in strict propriety, is entitled to the 

 name, and which consists in atrophy, or wasting of some of the 

 muscles of the larynx, especially the crico-arytaenoideus posticus. 

 In consequence of this wasting, the cartilages of the larynx fall 

 inwards at every inspiration, and the consequent diminution of 

 the" passage through which the air passes causes in respiration 

 a peculiar roaring, grating sound. If the ear be" applied to the 

 throat of a roarer, there may usually be heard at each inspiration 

 a grating flap, caused by the cartilage falling inwards. It is 

 important to observe that this sound, as also the roaring noise 

 accompanying it, occurs during 2?zspiration : for when such a 

 sound occurs during e:cpiration, it indicates a morbid condition 

 of the lower parts of the bronchial tubes. In roaring, the par- 

 ticular timbre or quality of the sound varies considerably, ac- 

 cording to the amount of the obstruction. Where this is very 

 great, and the diameter of the tube much reduced, a sharp 

 whistling noise is produced ; while, if there be less diminution 

 in the calibre of the tube, a deep roaring or grunting noise is 

 observed. Hence whistling is not in all cases, as is generally 

 believed, a less serious, but, on the contrary, is frequently a 

 much more serious, affection than roaring, resulting, as it often 

 does, from an aggravated state of the same morbid condition 

 on which roaring depends. Roaring may be readily detected, 

 even when not very bad, by giving the animal a gallop, which 

 renders the defect apparent by increasing the rapidity and 

 depth of the respirations, or by suddenly threatening to 

 strike the animal, or giving him a smart blow on the ribs, 

 which causes a sigh or deep-drawn inspiration, and thus gives 

 rise to the sound characteristic of the disease. Pressure on the 

 larynx also induces loud and repeated coughing, and in such 

 cases it is observable that each particular cough has a different 

 sound. 



Many cases, illustrating the hereditary nature of roaring, 

 might here be cited. The celebrated horse " Outcry" was well 

 known to be a roarer ; many of his stock, out of perfectly sound 

 dams, have turned out roarers; and I am informed, on com- 

 petent authority, that the defect of the sire has, in several in- 



