The proximity of the reticulum to the pericardium is also an important factor, because the foreign bodies fall into the reticulum as soon as the bolus of food begins to break up. It is important to notice, moreover, that pericarditis is commonest on farms where the oxen are attended by women, or in regions where sharp objects are to be found on roads or pastures frequented by the animals, such as the vicinity of needle, nail, and rivet factories.
The sole cause is the penetration of a foreign body into the pericardial sac.
Pathogeny. All kinds of foreign bodies are swallowed by oxen, as is abundantly shown by post-mortem examinations. These indigestible bodies pass with the food into the rumen, and accumulate in the deepest portions of that receptacle. Owing to physiological contractions the lower wall of the rumen rises to the level of the orifice of communication with the reticulum, and so passes much of the material accumulated within it into this organ.
Soft foreign bodies fall towards the lower parts of the reticulum, but sharp objects may lodge in its walls. Very often the bodies penetrate in this way without causing reticulitis or grave inflammation. The functions of the reticulum are not impeded. The commonest of such objects are needles, pins, nails, or fragments of iron wire. On account of their form, needles are the most dangerous. The sharpness of one extremity ensures its passing readily through the tissues, and as the point is the part that offers least resistance, the needle continues gradually to penetrate.
If the foreign body becomes implanted vertically in the lower wall of the rumen or reticulum it may be expelled directly through the medium of an abscess. This is a favourable termination, though it usually results in permanent gastric fistula.
More often the objects penetrate the anterior wall of the reticulum and gradually work their way towards the diaphragm, impelled by the movements of the reticulum and the other digestive compartments. They perforate the muscle and pass into the thoracic cavity, either in the direction of the pericardium or of the pleural sacs.
First as to the penetration of the pericardium. The foreign body, whatever it may be, produces by its presence alone very marked irritation, and as in addition it is always infected in consequence of its having passed through the digestive compartments, inflammation is set up to a degree proportionate to the pathogenic qualities of the infective agent.
Symptoms. The early symptoms are those of indigestion, and not of pericardial disease, a fact which is easy to understand, because at first the whole mischief is in the abdominal cavity. The patients are dull, restless, and seem to be suffering from an obscure ailment. They remain standing more than usual, show more than ordinary deliberation in lying down, lose appetite, cease to ruminate regularly, and exhibit intermittent tympanites.
The cause of these symptoms is as follows: At first the reticulum is partly immobilised by the local inflammation, and at a later stage movement of the diaphragm is checked by reflex action when the sharp body has progressed far enough to touch it. The rhythmic movements of the reticulum and the diaphragm are interfered with, rumination is disturbed, eructation ceases, and tympanites appears.
The patient often utters slight groans, particularly when forced to move; but as this is a sign common to all grave diseases it can only give rise to a suspicion as to what has occurred. In ten to fifteen days this primary phase may have terminated; but it is impossible to say how long it lasts, for it varies with each animal as with each variety of foreign body, and it may be prolonged for months.