Such secondary broncho-pneumonia only occurs when the diarrhœa has resisted treatment, and it is important to note that the pectoral lesions appear at a time when the intestinal mischief seems to have diminished, the diarrhœa having lessened or disappeared. This variety of broncho-pneumonia of young animals is by far the most frequent. It has been termed broncho-pneumonia of intestinal origin, and exactly resembles, so far as its development and gravity are concerned, the broncho-pneumonia in young infants described by Sevestre and Lesage.
The term broncho-pneumonia, moreover, is not strictly correct, or at least is not exclusive; for the rapid forms often exhibit lesions other than those of broncho-pneumonia. Post-mortem examination reveals pleurisy and pericarditis.
Pathogeny. At the outset of these attacks of broncho-pulmonary disease, a careful bacteriological examination of the organisms to be found in the discharge of bronchial mucus leads to the discovery of bacilli which do not stain with Gram, and which resemble varieties of the colon bacillus; in other cases of streptococci. At a later stage, when the animal has become weak, microorganisms are present in much greater variety. Nocard found in lung abscesses the bacillus of epizootic lymphangitis. It seems that the development of various lesions in the thoracic cavity may be due to auto-infection, i.e., to the penetration from the intestine of germs which, after passing through the circulation, establish themselves at some point in the lung. The pleura is attacked at a later period as a consequence of continuity and contiguity of tissue.
In a similar way pericarditis and even valvular endocarditis may be produced.
Symptoms. The symptoms are similar to those of all forms of broncho-pneumonia. Where diarrhœa has been neglected, the conditions may apparently improve without evident cause, whilst the respiration becomes more frequent. The patient soon suffers from cough, and in a few hours the existence of broncho-pneumonia is clearly apparent. Acceleration of breathing is the dominant symptom. The respirations may rise to fifty to sixty per minute, at which they continue, while fever sets in. On percussion the thorax may appear of normal resonance throughout; but when pleural lesions and exudates exist, resonance gives place to partial or complete dulness. Should pericarditis or small cardio-pericardial adhesions exist, they may escape observation, but if the exudate is abundant or the adhesions multiple or of large size the usual symptoms of pericarditis develop progressively.
On auscultation the respiratory murmur is always found to be greatly exaggerated in the healthy parts, usually the upper portions of the lung. On the contrary, it is attenuated or suppressed in the affected regions. The other signs vary greatly, according to the extent, intensity, and more or less advanced condition of the lesions. Crepitant and bronchial râles, blowing respiration and tubal souffles, etc., are among the symptoms.
The duration of the disease varies; some patients may be carried off in five or six days, while others survive for one or two months, or even longer. A few recover, but they remain thin, puny, and atrophied, and are not worth keeping alive.
Lesions. The lesions extend to the bronchi, the pulmonary tissue, and sometimes the pleura and pericardium. They consist in lesions of diffuse broncho-pneumonia, pleurisy with false membranes and parietopulmonary adherences, and pericarditis with partial cardio-pericardial adhesions.
In rare cases abscesses caused by pyogenic streptococci may be found.
The anterior lobes, cardiac lobes, and lower part of the posterior lobes are those singled out for attack.