The respiration, although regular whilst the animal is at rest, becomes accelerated on moving, and after attacks of coughing. It is sometimes rapid and whistling.
Percussion discloses neither partial nor complete dulness, but everywhere irregularly distributed mucous rattling and sibilant râles are revealed by auscultation.
There is no fever, the appetite is maintained, and, what is an even more important point, animals in good condition preserve their flesh. Interlobular pulmonary emphysema and emphysema resulting from dilatation are inseparable accompaniments of chronic bronchitis, for which reason the flank respiratory movement is frequently very marked.
The diagnosis is of only moderate difficulty, because although in certain conditions the disease may be mistaken for tuberculosis or emphysema, it can be distinguished by bacteriological examination of the discharge, by an injection of tuberculin, by careful auscultation, and by consideration of the general condition.
Lesions. The walls of the bronchi are thickened, the submucous connective tissue is sclerosed, the muscular fibres are modified in structure, and have become fibrous, while the epithelial layer is desquamated and suppurating. The peribronchial tissue also undergoes sclerosis, and in certain cases the smaller bronchi present marked dilatations resembling small caverns (bronchi-ecstasis).
Treatment can never be more than palliative; the aim should be to prevent the lesions becoming aggravated, and to check the pathological secretion from the bronchi, but the lesions already existent can never be removed. Tar water should be perseveringly administered. Essence of turpentine in doses of 2 to 2½ drachms per day in electuary (adults), creosote in doses of 1¼ to 1½ drachms, and terpine in doses of ¾ to 1 drachm give the best results, and produce a marked improvement.
PSEUDO-MEMBRANOUS BRONCHITIS.
The pseudo-membranous forms of bronchitis, formerly termed “croupal or diphtheritic bronchitis,” are rare. They develop suddenly or follow pseudo-membranous laryngitis. Like the latter, they are due to a specific infection, possibly aided by accidental causes.
Their causation is imperfectly understood, and they cannot be compared, still less homologated, with diphtheritic disorders in man. They are characterised by the formation of false membranes, which develop on the mucous surface, mould themselves over the internal surface of the large bronchi, and ramify throughout the bronchial channels like branches of trees. They are of greyish-yellow colour, and appear to be formed of fibrin, coagulated albumen, and epithelial débris cemented together with mucus.
Symptoms. At the outset these pseudo-membranous forms of bronchitis have the same characters as acute bronchitis, which at the crisis would be marked by the expulsion of fragments of false membrane by coughing. Most frequently it seems that the bronchitis follows its regular course, and in such case it is only during convalescence or a considerable time afterwards that the membranes begin to be discharged during paroxysms of coughing.