732 
PATHOLOGY OF BROKEN WIND IN HORSES. 
these fibres contract, diminish the calibre of the bronchial 
tubes, and press the air out of them. The diaphragm, with 
the thoracic, abdominal, and other muscles of the trunk, by 
contracting, press the air out of the lungs, and after them the 
muscular fibres of the bronchi contract, and still further press 
the air out, so that this forms the second movement, and com¬ 
pletes the act of expiration. In broken wind, however, the 
muscular fibres of the bronchial tubes do not contract, as the 
nerve which supplies them and regulates their action is para¬ 
lysed, and as a result of this the abdominal and other muscles 
have to take on their function, and hence the second movement 
of the flanks, so characteristic of this disease. 
The nerve which supplies the stomach and lungs is the par 
vagum or pneumogastric, and its functions are threefold, viz., 
motor, sensory, and ganglionic or nutrient. This is quite 
evidently the case, as the nerve is visibly larger after passing 
the petrossal ganglion; and as this nerve not only presides 
over the functions of the organs of digestion and respiration, 
but also sends branches, both motor and sensory, to the 
voluntary muscles of deglutition, &c. 
The first pathological change which takes place in broken 
wind is paralysis of the terminal extremities of the sensory 
filaments of this nerve on the walls of the stomach, and from 
want of tone and a due amount of nervous influence this organ 
becomes distended, its walls attenuated, and its functions 
impaired, or, indeed, almost suspended ; the paralysis extends 
thence along the course of the nerve towards the brain, and 
by reflex action the motor filaments wdiich supply the lungs 
are affected, so that they, and the muscular fibres of the 
bronchi with them, become paralysed, and atrophy and fatty 
degeneration is the result. In some cases rupture of the air- 
cells and emphysema may be established.” 
Again, in arguing against the mechanical theory of the 
influence of the stomach in causing broken wind, the Pro¬ 
fessor says:—“If broken wind was due to mechanical 
pressure of the stomach upon the lungs, then the inspiration 
would be laboured and expiration easy; but, on the contrary, 
the inspiration is very easy, and the expiration difficult; 
therefore I think, as I have already told you, that it is due to 
paralysis of the ultimate ramifications of the pneumogastric on 
the walls of the stomach, ’which paralysis extends and becomes 
reflected on to those branches of the same nerve which go to 
supply the lungs, and when these have become paralysed the 
functions of the lungs and bronchial tubes become impaired, 
so that the air cannot be properly expelled from them, ami 
hence the difficulty in expiration.” 
