Spontaneous herniæ are very rare in the domesticated animals. They occur only in aged animals, and various reasons have been suggested to explain their appearance. Certain herniæ of this character are only found in old female animals which have borne a considerable number of young. Repeated gestation produces elongation and relaxation of the muscular fibres from the weight of the fœtus and its envelopes. In time, the abdominal walls become thinner and thinner under the weight of the viscera, and thus facilitate the slow formation of a hernia. Certain practitioners consider that some of these spontaneous herniæ are due solely to the pressure produced by the distended viscera, as for example in greedy-feeding animals. In such cases the weight of the viscera would cause, as in the previous case, a certain degree of anæmia and emaciation of the abdominal muscles.
These spontaneous ventral herniæ are due in reality to changes in the nutrition of the abdominal wall, the exact cause of which it is difficult to ascertain. The elastic tunic becomes atrophied, and ceases to act as an automatic girth; the muscular wall gradually becomes sclerosed from the white line towards the sides, and having lost its elasticity becomes distended and thinned.
These changes are not exclusively caused by old age, for they may be found even in young animals.
Nothing can be done in cases of spontaneous herniæ. The qualities originally pertaining to the abdominal wall cannot be restored, and treatment is confined to applying suspensory bandages, and, where possible, preparing the animals for slaughter.
HERNIA OF THE RUMEN.
Causation. Hernia of the rumen is, as a rule, of traumatic origin, and always occurs in the left flank, either in the lower or middle regions. Cases of spontaneous hernia of the rumen have been observed in very old and anæmic animals, as well as in females which have borne many young and which have suffered from spontaneous progressive hernia of the uterus.
Symptoms. The symptoms are the same in all herniæ. Immediately after the injury the abdominal organs show a tendency to escape in the direction of least resistance. A fold of the rumen passes through the muscular fissure, and a swelling soon becomes visible externally, which alters the contour of the abdomen. Most frequently at this time traces of the injury can be detected on the surface of the skin, either the linear trace due to a horn thrust, the ill-defined lesion due to a kick, or what not. There follows rapid swelling, which results from the inflammatory reaction due to rupture of small vessels within the muscle. A certain amount of sanguineous exudation and of œdematous swelling occurs, and may at first suggest the existence of an abscess of the abdominal wall. At the same time there is more or less fever, which may continue for a few days, but the swelling seldom lasts very long; in two or three days even, it becomes reabsorbed, commencing at the upper part and diminishing progressively downwards.
Henceforth the hernia alone remains.
It is soft, compressible, and sometimes susceptible of reduction. On palpation, the operator feels a rupture extending through the tunic and the abdominal wall, sometimes even through the muscular tissue of the rumen, in cases where the skin is neither perforated nor torn through. The mucous membrane of the rumen is rarely ruptured.
Whether or not the peritoneum is injured, the rumen presses between the lips of the wound, thrusts back the skin, and separates the connective tissue, thus setting up local irritation and œdematous swelling. The rumen may contract more or less close adhesions with the abdominal wall, and even with the subcutaneous tissues.