Distemper is not peculiar to any age; the young and old are equally exposed, although the favourite period for the attack is between the sixth and twelfth month; or during the period of second dentition, at whatever age that may take place. The disease is always most severe and fatal when it attacks young puppies of the smaller breeds.

One attack does not altogether exhaust the susceptibility to another, or to other attacks; it has, however, a certain preservative and modifying influence.

* Holmes' System of Surgery. Vol. iii.

The disease prevails in summer, more so in spring, most so in autumn, when diarrhoea is a frequent and troublesome complication.

It is both endemic and epidemic - in the former confining its ravages within the limits of certain districts; in the latter, spreading wide and far. Different epidemics of the disease are characterized by particular local complications; in one, the bowels are chiefly involved, in another, the respiratory organs, and in a third, the nervous system.

The disease is undoubtedly contagious, although some dogs escape it just as some human beings escape fever or cholera. Dogs that are pampered and confined suffer from distemper more severely than others.

The most frequent exciting causes are exposure to damp and cold, and whatever induces debility of the system, such as rickets, mange, catarrh, etc.

Symptoms

The symptoms present considerable variations, which depend upon the rapidity of the disease, the character of the prevailing epidemic, and the local complication; but they all show that the disease is essentially a low fever, accompanied by prostration of strength and wasting, with a strong tendency to some particular local lesion.

The onset of the attack is either sudden, or gradual, generally the latter. In the earliest stage, the dog is observed to be dull and depressed, and takes no notice of food, or of his owner; there is sometimes vomiting and purging, but usually these symptoms do not come on until a more advanced period. In a short time, a scanty, clear, and watery fluid issues from the nose; the eyes are watery and unusually sensitive to light; and the animal has a short, dry, husky cough, which appears as if provoked by irritation in the throat, and is aggravated by exertion. The dog is observed to give an occasional sneeze. In a morning, there is a slight moisture, or perhaps a little dry mucus, at the corner of each eyelid; and the everted lid is rather more vascular than usual. The pulse is slightly increased in frequency - from 110 to 130 per minute, according to the patient's age. There is evident prostration of the nervous and muscular systems, progressive emaciation and no appetite. These catarrhal-like symptoms may lead the owner to suppose that the disease is nothing more than a simple "cold," but the dog's age and the prevalence of distemper will naturally arouse suspicion.

As the disease advances, fresh symptoms appear and existing ones become aggravated. There is constant shivering, accompanied by aversion to cold, and preference for warmth; the coat stares; the bowels are either relaxed or confined, and the faeces dark; the urine is scanty and high-coloured; the pulse is still more frequent and compressible; the temperature of the surface, and especially of the paws higher; and frequently an offensive vomit comes up from the stomach. At the same time, the nasal discharge assumes a purulent character, and increases in quantity; it adheres to the nasal orifices and obstructs respiration, much to the patient's annoyance: the respiration is quickened; and the cough is short, almost constant, and sonorous. On listening to the chest, the respiratory murmur is found diminished in intensity, and somewhat obscured by mucous rattles. These symptoms show that the disease has travelled along the mucous membrane from the nose to the air-tubes, and that bronchitis is established.

Recovery, indicated by subsidence of all the symptoms and by return of appetite, may now take place; or the disease may run on to pneumonia. This event is known by the pulse remaining quick and becoming weak, the thick nasal discharge forming adherent crusts, and perhaps mixed with streaks of blood; and the respiration getting more and more difficult and laborious. The cough generally continues, and brings up rusty-coloured mucus. The most marked sound heard in the lungs is the tubular respiration which denotes consolidation of the pulmonary parenchyma. Death almost invariably happens in such cases, either from the severity of the lung lesion interfering with the function of respiration, or from exhaustion consequent upon the general disease.

Of the several complications which come on during the course of distemper, conjunctivitis and keratitis are the most common; and they appear, unlike the others, at an early stage of the primary disease. At first, the eyes are watery and intolerant of light, and a slight mucous discharge exudes between the lids. The vessels of the conjunctiva are unusually distinct, both on the globe of the eye and on the inner surface of the lids. The discharge soon assumes a purulent character, and when abundant runs down the face. The lids are frequently agglutinated, especially in the morning, and the photophobia is extreme. In those cases in which the inflammation extends to the cornea, a general cloudiness gradually comes over the cornea, rendering it opaque and white, and, of course, impairing vision. Then in the centre of the cornea, or towards one side, there appears a circular ulcer, at first minute, but gradually extending in depth and width. Minute abscesses sometimes form between the layers of the cornea. The ulcer at last penetrates the cornea, the aqueous humour escapes, the iris protrudes, and the extreme pain is relieved. When the distemper yields, these affections of the eye gradually subside, and the ulcer heals up, leaving only a small speck, which generally disappears after a little while.