588 HEREDITARY DISEASES OF IIORSES. 
might here be cited. The celebrated horse c Outcry' was 
well known to be a roarer ; many of his stock, out of per- 
fectly sound dams, have turned out roarers ; and I am 
informed, on competent authority, that the defect of the 
sire has, in several instances, been very evident in the third 
generation. Some time ago, a friend of my own got from 
Northumberland two young horses of considerable value. 
Though perfectly sound at the time of purchase, both soon 
after became roarers : they had been bought from different 
breeders, but, on inquiry, it was found that both were got by 
the same sire, and that many more of his progeny had also 
become affected by the same disease. 
But roaring may occur independently of hereditary causes. 
It is occasionally produced by the presence of tumours in the 
larynx or trachea ; more often by constrained positions of 
the head and tight reining, and hence frequently occurs in 
old carriage-horses. It is sometimes met with in crib-biters, 
from their being made to wear straps buckled too tightly 
round the throat. It supervenes from bad attacks of bron- 
chitis, especially when of frequent occurrence, and also from 
phlebitis, being caused in the latter instance by defective 
nutrition of the muscles of the larynx. But even in cases 
where roaring is not congenital, but is produced during the 
lifetime of the animal, and by accidental causes, it may 
manifest a hereditary tendency. There is, indeed, no acci- 
dental defect more commonly transmitted from parent to 
offspring than that on which roaring depends. 
Considerable caution is requisite in judging as to the 
existence of roaring in stallions of the heavier breeds, for 
three fourths of these, when briskly exercised, produce a 
loud roaring noise, which often occurs without any disease of 
the larynx, trachea, or any part of the respiratory apparatus. 
It results from the high spirit and condition in which entire 
horses are usually kept, from the acute angle at which they 
generally carry the head, the abundant disposition of cellular 
tissue and fat about the throat, the comparatively small 
width between the sides of the lower jaw, the great develop- 
ment of the muscles of the neck, and the thickness of the 
mucous membrane lining the larynx and contiguous parts. 
But the noise so produced is somewhat different from that 
depending upon morbid peculiarities. It is observed during 
expiration as well as inspiration, and usually disappears 
w*hen the nose is elevated so as to be placed as much as 
possible in a line with the neck. When the sound has these 
distinguishing characters, and occurs in animals of the 
heavier breeds with well-formed necks and chests, it is 
