Causes are all such as induce catarrh, or inflammatory conditions of other parts of the respiratory apparatus. It may arise as a sequel to pulmonary congestion, or be induced by direct irritation of the air-tubes, as when medicines, in being given, "go the wrong way". It also follows on bronchitis by a downward extension of the inflammation into the substance of the lungs. Neglected colds and damp unhealthy stables are among the most frequent of the many causes that contribute to this disease. Influenza and strangles not unfrequently terminate in a fatal pneumonia, and there is reason to believe that the disease is sometimes in itself specific and contagious. In this connection it has often been noticed to spread from animal to animal in the entire absence of any obvious cause of a common character. Septic pneumonia, such as occurs in the "joint ill" of foals, and other forms of blood-poisoning, is by no means an uncommon variety of this disease.
There is a train of symptoms that may be called common to all inflammatory disorders of the respiratory system, and only the expert can, with any degree of accuracy, distinguish between them. Following upon catarrh, it cannot be said precisely when pneumonia commences, but there will be increased temperature and accelerated breathing, though in the latter connection not to the extent observed in acute pulmonary congestion. The mucous membranes exhibit a rusty or brick-red colour, and the pulse is small and irritable. The skin and extremities will be more or less cold, but scarcely with the icy coldness of acute congestion, nor will the sweating and trembling of that condition be present as a rule.
There is very little appetite, a tendency to constipation, and the urine is highly coloured and small in quantity. While the cough of a common cold and of bronchitis is accompanied with a more or less considerable discharge of mucus from the nostrils, there is but little in pneumonia, and what there is is thin and frothy, but as the disease advances there is a foetid odour to the breath, and the matter expectorated is more or less reddened from admixture with spoilt blood and other decomposing material.
If the chest sounds are listened to throughout an attack they will at first be observed to be louder and harsher than in health, hut as the air-tubes become charged with inflammatory products they undergo modification and give out minute crepitant or crackling sounds. When the air-cells and small tubes become actually filled with these products, and air is altogether excluded, crepitation ceases as a result of consolidation of the lung substance. The bronchial sounds in the upper part of the chest, however, are more or less exaggerated. Percussion applied to the chest by means of the fingers will enable us to make out with more or less accuracy the part of the lung which has undergone solidification, as there is an absence of resonance over the part where no air passes in or out. In speaking of congestion of the lungs, the rapid progress of the disease has been referred to, and in this it differs from pneumonia, which may take a week in reaching a crisis, and probably two or more weeks before the symptoms have quite disappeared, a high temperature being-maintained for many days. Relapses of a febrile character, at a time when considerable progress has been made, are not uncommon, and would seem to be due, in many instances, to infection of the blood with morbid matter, resulting from the disintegration of lung tissue.
Before determining what method of treatment should be adopted, it is well to consider the history of the individual and the circumstances that have led up to the illness. Also his condition, whether it is one of poverty and weakness - if the animal is an aged one or a young and full-blooded creature fresh from the liberty of pasture. These and other circumstances affecting individuals will materially influence the line of treatment to be pursued. In the former case we should not recommend measures of depletion of any kind, but in the latter these might with advantage be sometimes employed. In dealing with this disease modern practitioners attach much more importance to hygienic conditions than used to be the case. Good nursing, the maintenance of an equable temperature, both of the skin and stable atmosphere, scrupulous cleanliness, ample ventilation, and judicious feeding have now become recognized as indispensable to successful treatment. Friction of the body and extremities, the employment of suitable clothing and bandages, frequently removed and replaced, are not less Important, Saline febrifuges are generally approved, and of these acetate of ammonia, nitrate and chlorate of potash, and sulphate of magnesia judiciously administered are the most appropriate.
Plenty of bland mucilaginous fluids, as linseed tea and barley-water, and an unlimited quantity of drinking-water, should be allowed. When the febrile symptoms have abated, and extreme prostration or foetid breath has to be combated, there is benefit to be anticipated from the use of quinine, with the free use of alcoholic stimulants, as whisky, port-wine, or good ale, and the animal's strength will be most speedily regained under the influence of such things as beef-tea. eggs, and milk. The methods of administering the agents named will depend upon the presence or otherwise of irritability of the throat. Where this is great, with much cough and difficulty in swallowing, electuaries may be chosen, unless the patient can be induced to take them in drinking-water. In all pulmonary affections, draughts require to be administered with the greatest care, and in some instances must be altogether withheld. Where it is found necessary to adopt the latter course, spirit of wine in ounce or two-ounce doses may be administered in the drinking water as often as may be required. Want of appetite after a severe illness of this kind is a troublesome feature, and the old remedy of gentian, either in the form of powder or of compound infusion, with a mineral acid, as sulphuric or nitro-hydrochloric, afford the best results.