DIAGNOSIS AND PROGNOSIS OF HERNIA. 
265 
increase abdominal pressure and render it larger; but it decreases when 
intra-abdominal pressure again falls. 
(c) It is reducible, that is, the swelling may completely disappear on 
pressure, or on placing the animal in a suitable position, but it returns 
on removal of pressure or alteration of position. 
Diagnosis only becomes absolute when the hernial opening is dis¬ 
covered. It can generally be felt by thrusting a finger into the depth 
of the sac, especially after reducing the hernia. Examination per anum 
is sometimes useful in horses and oxen ; the hernial ring and the con¬ 
tained bowel may be felt; by traction on the bowel the hernia can 
sometimes be reduced. Exploratory puncture may also be resorted 
to in otherwise doubtful cases. Some care is required to differentiate 
hernia from abscess or hsematoma, an error which might have grave 
consequences, as already pointed out in speaking of bruises of the 
abdomen. 
Prognosis. Hernia itself is not fatal, but immediately strangulation 
occurs it becomes exceedingly dangerous. Prognosis chiefly depends on 
the probability of strangulation, a factor which will be considered in 
speaking of the various hernise. The smaller the hernial aperture 
compared with the size of the sac, the greater the danger of strangulation. 
Small intestine becomes more easily strangulated than colon or omentum. 
The size of the aperture, and the use to which the animal is put, must be 
considered, whilst it should be remembered that strangulation occurs 
more easily in working-horses, and that large hernise may interfere with 
usefulness. 
Many hernise, and especially umbilical and inguinal hernise in young 
animals, disappear without treatment, and others may last the animal’s 
whole life without interfering with its use. 
Irreducible hernise are more dangerous than reducible, recent than 
old, and intestinal than omental, because in each case the former are 
more likely to become incarcerated than the latter. We shall speak further 
on this head in describing the various hernise. 
Strangulation or incarceration is the condition in which the hernial 
ring presses on the contents and interferes with normal circulation of 
blood and passage of ingesta through the intestinal loop. It consists, 
then, in ligation of the contents by the hernial ring, producing stasis of 
fseces and disturbance of circulation and nutrition. In consequence of the 
pressure of the hernial ring on the contents, return of blood through the 
venous vessels is first checked. In them blood-pressure is lower, and 
the walls weaker, and therefore circulation is more easily interfered with 
than in the arterial vessels, whose strong walls and high blood-pressure 
oppose considerable resistance to compression. Blood continues, there¬ 
fore, to enter by the arterial vessels even after strangulation, and soon 
