378 
RESPIRATION. 
traying it by any very remarkable outward signs, is a circum- 
stance of ordinary occurrence. But irritation of the stomach, 
intestines, and liver, likewise take place of that degree of force 
and activity, and which is prolonged and kept up for a consider- 
able time, undefined by any limits of duration, and productive of 
very important effects on the ganglionic nervous system and the 
cerebro-spinal axis. 
Between the alimentary digestive tube and the respiratory 
organs there is a nervous relationship, by which an association 
of sympathies is maintained, and a co-operative influence pre- 
served of the highest order in the animal economy. Disorder of 
the digestive mucous surface in association with affections of the 
organs of respiration, is a complication of morbid changes daily 
illustrated in veterinary practice. Catarrh, bronchitis, and pneu- 
monia are complications of the active forms, and chronic cough, 
verminous cough, and broken wind are of the sub-acute order, 
serving to evince the complication of disorder existing between 
the respiratory and digestive and assimilating organs. 
It is through the operations of the nervous system primarily, 
and the circulating system secondarily, that we can explain two 
important facts relative to roaring, viz., the hereditary transmis- 
sion of the malady from the parent to the offspring, and the cir- 
cumstance of tall horses with long necks and extended forehands 
being more the ordinary subjects of it than those of conformation 
just the reverse. Every horse-dealer is acquainted with the latter 
particular, and has his suspicion always awake to the event in 
purchasing lofty horses with ranging forehands ; while with the 
horse of short stature and compact conformation he is less ap- 
prehensive of the affection. The hereditary predisposition to 
roaring is dependent upon original conformation. It is not to be 
supposed that the foal comes into the world with the disease ex- 
isting in a latent form, and ultimately developed by the various 
exciting causes ; but it is generally observed that the offspring 
resembles the parent in conformation, constitution, temper, and 
disposition to disorder, whether of structure or function. Many 
horses in stable treatment are subject to cough from slight ex- 
posures to variable temperature, from which others would suffer 
no inconvenience. Others have active inflammation in the mu- 
cous and submucous tissues of the larynx, followed by resolution 
and perfect restoration of those structures to their normal con- 
dition. Not the least alteration in the laryngeal murmur is the 
consequence; but with others, on the subsidence of the increased 
vascular action, a contraction of the laryngeal passage is found 
to have taken place, and roaring or whistling is permanently 
established. 
