Symptoms.—As in dogs, both furious and dumb rabies are met with, the former being more common in cattle. A sharp line of distinction, however, can not be drawn between these two forms of the disease, as the furious form usually merges into the dumb, from the paralysis which appears prior to death. The typical cases of dumb rabies are those in which the paralysis appears at the beginning of the attack and remains until death. The disease first manifests itself by a loss of appetite and rumination, stopping of the secretion of milk, great restlessness, anxiety, manifestation of fear, and change in the disposition of the animal. This preliminary stage is followed in a day or two by the stage of excitation, or madness, which is indicated by increasing restlessness, loud roaring at times with a peculiar change in the sound of the voice, violent butting with the horns and pawing the ground with the feet, with an insane tendency to attack other animals, although the desire to bite is not so marked in cattle as in the canine race. A constant symptom is the increased secretion of saliva with a consequent frothing at the mouth, or the secretion may hang from the lips in long strings. Constipation is marked, and there is manifested a continual, although unsuccessful, desire to defecate. Spasms of the muscles in different parts of the body are also seen at intervals. About the fourth day the animal usually becomes quieter and the walk is stiff, unsteady, and swaying, showing that the final paralysis is coming on. This is called the paralytic stage. The loss of flesh is extremely rapid, and even during the short course of the disease the animal becomes exceedingly emaciated. The temperature is never elevated, it usually remaining about normal or even subnormal. Finally, there is complete paralysis of the hind quarters, the animal being unable to rise, and but for irregular convulsive movements lies in a comatose condition and dies usually from the fourth to the sixth day after the appearance of the first symptom.
Anatomy.—If animals which have succumbed to rabies are examined post mortem, very slight evidence of disease will be found in any of the organs, and, indeed, the absence of any specific lesions may be considered as characteristic. The blood is dark and imperfectly coagulated. The throat is frequently reddened, and there may be small spots of extravasated blood in the intestines. The stomachs are usually empty. In the spleen there may be hemorrhagic enlargements (infarcts). The cadavers rapidly undergo decomposition.
Differential diagnosis.—It is not an easy matter to decide definitely that a given animal has rabies, since the symptoms given above belong in part to a variety of other diseases, among which may be mentioned the excitement seen in young animals following close confinement, certain vegetable and mineral poisons, acute enteritis, and alterations of the central nervous system in cattle, the most common of which is tuberculosis of the brain and its covering membranes. The post-mortem lesions, however, should assist in making a correct diagnosis. Tetanus may readily be differentiated from rabies by the persistence of muscular cramps, especially of the face and abdomen, which cause these muscles to become set and as hard as wood. In tetanus there is also an absence of a depraved appetite or of a willful propensity to hurt other animals or to damage the surroundings. The cow remains quiet and the general muscular contraction gives her a rigid appearance. There is an absence of paralysis which marks the advanced stage of rabies. The form of dumb rabies in dogs is characterized by the paralysis and pendency of the lower jaw, while in tetanus the jaws are locked. This locking of the jaws in cattle renders the animal incapable of bellowing, as in rabies. Finally, tetanus may be distinguished from rabies by the fact that the central nervous system does not contain the infectious principle, while in rabies the inoculation of test rabbits with the brain or cord of a rabid animal will produce the disease with characteristic symptoms after an interval of 15 to 20 days. This period of incubation is much longer than in tetanus, since the inoculation of rabbits with tetanus cultures invariably results in death after a short period and usually within three days. The positive evidence that a rabid dog has been near cattle would greatly assist in making a decision in doubtful cases.
The disease in dogs is pretty well recognized by most people, but in case a suspected dog is killed it is desirable to open the animal and examine the contents of the stomach. While feed is absent, a variety of odd things may be present which the abnormally changed appetite of the rabid dog has induced it to swallow. Among such things may be straws, sticks, glass, rags, earth, pieces of leather, and whatever the animal may have encountered small enough to be swallowed. This miscellaneous collection in the stomach of dogs, together with absence of feed, is regarded by authorities as a very valuable sign, and in case of doubt may be made use of by laymen. In important cases, however, the head of the dog, cow, or other suspected animal should be removed and sent to the nearest biological laboratory, where a positive diagnosis can be made within 36 hours by the histological examination of the plexiform nerve ganglia, and within two or three weeks by the intracerebral inoculation of rabbits with an emulsion of the brain of the suspected animal.
Treatment.—This is useless after the first appearance of symptoms. When, however, a wound inflicted by a rabid animal can be discovered, it should be immediately cauterized or even completely extirpated, care being taken to cut entirely around the wound in the healthy tissues. For cauterizing the wound, fuming nitric acid, the hot iron, and 10 per cent solution of zinc chlorid are the most efficacious. To afford an absolute protection, this should be done within a few moments after the bite has been inflicted, although even as late as a few hours it has been known to thwart the development of the disease.
Pasteur originated and perfected a system of preventive inoculation against this disease which has greatly reduced the mortality in human subjects. Its application to animals, however, is difficult and requires considerable time and expense. A method of vaccination applicable to animals, consisting of a single injection of a suspension of "fixed" rabies virus, is now being quite extensively employed by veterinarians. Sanitary regulations which seek to control effectively the disease by exterminating it among dogs are most likely to prove successful. The measures which are adopted to this end can not be discussed in this place, but it is a striking fact that where the muzzling of all dogs has been rigidly enforced, as in England and in certain German districts, the disease has been practically stamped out.
TUBERCULOSIS.
[[Pls. XXXIV]-[XXXVIII].]
Tuberculosis is an infectious and communicable disease characterized in its early stages by the formation, in various organs of the body, of minute nodules or tubercles, which contain Mycobacterium tuberculosis, the cause of the disease.