EOARINGr. 385 



tuated to perform labour demanding extreme exertion of tlie organs 

 of brea tiling. 



3. Size of Jiurse. — Tlie paralytic form of roaring is, essentially, 

 a disease of large horses. Although ponies are as liable to become 

 broken-winded as are big animals, they very seldom contract this 

 form of roaring. We find among horses which are own brothers 

 and sisters, and which have an hereditary taint, that the bigger 

 the individual animal, the more predisposed it is to roar. The 

 only explanation which I can offer of this fact, is that the smaller 

 the horse, the quicker is the circulation of blood, and, consequently, 

 the readier will be removed from the system any diseased products 

 formed during an attack of catarrh, strangles, etc., which might 

 become absorbed into the lymphatic glands of the neck, and thus 

 give rise to injurious pressure on the left recurrent nerve. No 

 breed of pony, as far as I know, possesses absolute immunity from 

 roaring, which I have observed in English, Australian, Arab, East 

 Indian, and Chinese ponies. 



4. Stable arrangements that are calculated to induce coughs and 

 colds; such as those which obstruct ventilation and give rise to 

 draughts of cold and damp air. While living in St. Petersburg a 

 few years ago, I saw very strong evidence of this influence among 

 fashionable llussian carriage-horses, which were kept in hot, ill- 

 ventilated stables, and consequently many of them suffered from 

 roaring. The common horses, which had a full supply of fresh 

 air, even when the thermometer went down to — 30° F., were 

 practically free from this disease. 



5. Violent exertion of the organs of breathing. — It goes without 

 saying that the more any organ is over-taxed, the more liable will 

 it be to become diseased. 



6. Insufficient exercise of the muscles of the throat. — Mr. Henry 

 Goodall, M.R.C.V.S., observed to me that as the horse is constituted 

 to spend a large portion of his time with his head close to the 

 ground when feeding, during which period the muscles of his head 

 and neck are in almost constant exercise; the practice of tying 

 up stabled horses and feeding them from raised mangers, must 

 injuriously affect the muscles which open the larynx by diminish- 

 ing their blood-supply. A dependent position of the head and 

 the fact of the surrounding muscles being in play, would naturally 

 increase the blood-supply of the part. In India and South Africa, 

 horses are, however, tied up and fed from raised mangers the same 

 as in England. 



PERIOD OF INCUBATION IN PARALYTIC ROARING.— 



Dieckerhoff considers that the period of incubation is not less than 

 a month. He has arrived at this conclusion, from careful observa- 



25 



