EOARING. 383 



hard food; and being habituated to perform labour demanding 

 extreme exertion of the organs of breathing. 



3. Size of Horse. — The 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 roaxing. Among horses which are own brothers and 

 sisters, and have an hereditary taint, the bigger the individual 

 animal, the more predisposed it is to roar. The only explanation 

 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 roar- 

 ing, 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 Petrograd a 

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

 fashionable Russian caj-riage-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. — ^As the 

 horse is constituted to spend a large portion of his time with his 

 head close to the gro'und 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 diminishing their blood-supply. A dependent positiom 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- 

 tion and from the fact that when roaring occurs, as it not in- 



