Causation. The conditions under which food is swallowed by ruminants after preliminary mastication permit indigestible objects, such as stones, fragments of wood, nails, needles, bits of iron wire, etc., to enter the rumen, whence they reach the reticulum in consequence of peristaltic movements. Sharp, perforating objects, like needles or fragments of iron wire, penetrate the walls of the gastric compartments, and, impelled by the movements of these organs, pass through the intervening tissues, usually in the direction of the heart. Under conditions which cannot precisely be defined, these foreign bodies make their way towards the pleural cavity (usually the right, in consequence of the situation of the reticulum), traverse the diaphragm, and directly penetrate the base of the lung.
As the migrating object is usually infected, its passage through the diaphragm always produces a localised patch of diaphragmatic pleurisy. Although possible, it is only rarely that the pleural sac becomes generally infected, or that rapidly fatal septic pleurisy is set up. Usually the localised pleurisy causes the base of the lung to become adherent to the anterior surface of the diaphragm. The foreign body continuing its movements, passes into the lung, and there sets up pneumonia.
Symptoms. When the practitioner is first consulted he often finds only indications of the crisis period of a localised pneumonia at the base of the affected lung. The symptoms include fever, accelerated breathing, moaning, loss of appetite, cough without discharge, dulness over the base of the lung on percussion, disappearance of the respiratory murmur in the dull area, souffle opposite the inferior bronchi, and normal or juvenile respiration towards the front, i.e., in the anterior lobe, and sometimes in the cardiac lobe.
The temptation under such circumstances is to deliver a diagnosis of simple pneumonia with prognosis of probable recovery. It should be remembered, however, that in all cases of basilar pneumonia without affection of the anterior lobes there is a considerable chance of the condition being due to the presence of a foreign body. On more careful examination it is found that the intercostal spaces opposite the affected region are very sensitive, and that the circle of the hypochondrium is correspondingly sensitive. The owner, moreover, almost always informs the practitioner that for several weeks his animal has coughed, shown tympanites, diminished appetite, etc.
Compression of the roots of the corresponding diaphragmatic nerve at the base of the neck always produces coughing.
These symptoms rarely accompany the development of simple pneumonia. Furthermore, the course of this accidental pneumonia is entirely different. Instead of developing regularly according to the above-described cycle, pneumonia due to foreign bodies develops slowly, and only becomes well defined after several weeks, whilst its tendency is to grow more and more aggravated. The zone of dulness extends both in a forward and upward direction. The souffle extends forwards. Auscultation and palpation sometimes reveal the formation of an abscess or local gangrene; while there is slight œdema of the wall of the chest, as well as a gurgling sound at the moment when the lung is displaced, high fever, intensely coloured urine, and very marked leucocytosis, etc. Death is inevitable, and when gangrene exists it sometimes occurs suddenly.
Diagnosis. The diagnosis is based on the information furnished with regard to the course of the disease, the localisation of the hepatised zone, and the progressive character of the affection.
The diagnosis, nevertheless, is always a little doubtful, but may be so far assured as to attain the position of a quasi-certainty.
Prognosis. The prognosis is unequivocal.
Treatment. No practical treatment, either to extract the foreign body or to combat the special pneumonia which it has produced, can be attempted. All the interlobular connective layers and the lobules themselves are invaded by various microorganisms carried by the foreign body. Numerous fragments of tissue serve as centres of suppuration and gangrene, and the only chance would lie in attempting resection of the lung. Such intervention has no practical interest in veterinary surgery. It is true that when the existence of an abscess is suspected, an aseptic exploratory puncture may be made, and, in the event of the diagnosis being so far confirmed, the abscess might be opened through an intercostal space. Under such circumstances, however deep the point of penetration of the foreign body, the development of the resulting abscess causes local pleurisy and adherence between the pleura and lung, so that there is no immediate danger of producing purulent pleurisy and pneumo-thorax. If small the foreign body might possibly be discharged through the passage thus afforded.