224 WOUNDS OF THE PLEURA AND THORACIC CAVITY. 
examination and checking haemorrhage are applicable in wounds extend¬ 
ing under the shoulder. Arrangements must be made for the easiest 
exit of discharges, and incisions, counter openings, drains, &c., combined 
with effectual irrigation, adopted as above indicated. 
(2) WOUNDS OF THE PLEUEA AND THORACIC 
CAVITY. 
Punctured or penetrating wounds of the cnest are usually caused by 
thrusts with the bayonet, lance, or sabre ; in war by projectiles; by 
falling on harrow teeth, or on the rider s spur; in oxen by hom-thiusts, 
by splinters of wood, or by the aspirating needle used to drain the pleural 
sac. Such wounds may extend through the pleural costalis, and even 
injure the thoracic or abdominal organs. Besides the dangers of bleed¬ 
ing and infection, such injuries may lead to pneumothorax, hsemothorax, 
pleurisy, and pneumonia. 
(1) Pneumothorax. Air may enter the pleural sac either from without, 
or from the lung. As soon as a considerable wound penetrates the 
pleural costalis, the distended elastic lung generally collapses, air is 
drawn in through the opening in the pleural sac, and bieathing ceases 
in the affected portion of lung. The walls of the chest continuing 
their respiratory movements, however, the an stieams outvaid during 
expiration, and re-enters during inspiration. Should the opening in the 
thoracic wall be partly or entirely closed during expiration, emphysema 
results from the retiring air being forced into the loose connective 
tissue in the neighbourhood of the wound. Injury to lung or a bronchus 
also causes pneumothorax, usually attended with severe bleeding and 
collapse of the affected portion of lung. 
Air in the pleural sac is not necessarily fatal, so long as both lungs do 
not collapse, though in the horse such a complication is to be feared on 
account of the cribriform nature of the mediastinum behind the heart. 
It is reabsorbed in a comparatively short time, as has long been known 
in man ; and more recently been demonstrated in horses by the experi¬ 
ments of Trousseau, Leblanc, and Perosino. Perosino opened the 
pleural sac in a horse between the 10th and 11th ribs, and allowed 
air to enter through a tube until the difficulty in breathing threatened 
death from suffocation ; but, on the evening of the day of experiment, 
all untoward appearances had vanished. Pneumothorax is, nevertheless, 
a very grave condition, because infectious material, entering with the 
air, may produce severe inflammation. Air, entering the thorax through 
wounds, is more apt to be infective than that admitted through the lungs, 
which is purified as it passes over the respiratory mucous membrane, 
much in the same way as air entering a bottle may be filtered by a 
