266 
PROGNOSIS OF STRANGULATED HERNIA. 
produces a severe venous congestion, usually associated with more or less 
extensive rupture of small vessels and haemorrhage. Blood-stained serum 
is exuded, the hernial fluid increases, and in consequence of mixture with 
blood becomes red in colour. The hernial contents, especially the serosa 
of the intestine, is dark red or black, and this coloration is distinctly and 
usually sharply bounded by the ring-like circle of compression, which 
is grey and anaemic. Both this anaemia and the venous congestion 
impair nutrition in the strangulated parts, and may finally produce 
necrosis. 
The faecal stasis adds to the disturbance thus produced, because the 
imprisoned intestinal contents putrefy, irritate the mucous membrane, 
and co-operate with defective circulation in producing necrosis of the 
mucous membrane. Infectious materials and their products possibly play 
a certain role here. 
Necrosis first shows itself at two points, viz., in the deepest portion 
of the hernial contents, where circulation suffers most, and at the line 
of strangulation. It is well to remember, from the clinical standpoint, 
that dark colour is not always a proof of necrosis. The latter is usually 
typified by the presence of grey spots or patches on the surface of the 
peritoneum, or of ulcerative changes in the hernial contents. Necrosis 
is suggested by the presence of stinking fluid or gas in the hernial sac. 
The anterior portion of the bowel—that is, the part nearest the stomach 
—appears greatly distended with food, whilst the posterior portion is 
empty and narrower than normal. 
Causes. Strangulation was formerly believed to be produced by spas¬ 
modic contraction of the hernial ring ; but, apart from the fact that in most 
ruptures such contraction seems scarcely possible, it is not to be imagined 
that active contraction could continue so long. Such views are no 
longer entertained, and the cause of strangulation is to be sought rather 
in the character of the hernial contents. Inflammatory swelling near 
the neck of the hernia may in exceptional cases cause incarceration, but 
is exceedingly rare. The primary factor in incarceration is usually 
increase in the hernial contents; conversely this increase may be a 
result of incarceration. Let us imagine a case: A horse affected with 
hernia suffers from tympanites ; the increased intra-abdominal pressure 
thrusts a large portion of bowel and omentum from the abdominal cavity 
into the hernial sac ; on account of the increase of the hernial contents 
the ring becomes too narrow; it presses on the enlarged contents and 
interferes with circulation in the parts which it surrounds, and incar¬ 
ceration results (figs. 121 and 122). Or let us fancy that in the posterior 
portion of the intestinal tube—that is, in the portion through which the 
intestinal contents are returned from the hernial sac into the abdominal 
cavity—some check occurs, causing fiecal stasis. Necessarily the hernial 
