The antiquity of hydrophobia is not precisely known. Aristotle is the first author to mention this malady, but his account of it is remarkably incorrect, if the text be not corrupted. He says, "all animals that are bitten by a rabid dog are affected with the disease except man; and that the disease proves fatal to all animals but man".

Among the ancient anthors Caelins Anrelianns treated all the important questions relating; to hydrophobia in a most masterly manner. Alter him centuries passed during which, with but few exceptions, independent observations ceased, and little or nothing was added to the previous knowledge on the subject.

Investigations were renewed towards the end of the last century by Hunter and other intelligent observers, and recently a more exact knowl. edge of the disease has been acquired through the studies and experiments of Hertwig, Heynell, Youatt, Magendie, Blaine, Virchow, Reder and others.

Hydrophobia or more properly rabies, which prevails chiefly among animals of the canine species, ( dog, wolf; fox, jackal ) is at the present time accepted as being an acute infectious disease, coming on in the form of a functional disturbance of the central nervous system, without structural changes which can be considered essential to the affection.

Examinations after death have revealed in most cases diseased appear, ances, but not one has been found to be present invariably, and no local changes have been discovered which could explain all the symptoms.

Causation

The theory of a spontaneous development of rabies so frequently advanced, has been rejected as entirely unfounded by very many of the most intelligent observers, recent as well as old.

It is unnecessary to enumerate and describe all the influences which, have been cited as predisposing and accidental causes; in wearisome arguments our best authorities have proved the theories untenable and unfounded, and that all the causative conditions such as seasons of the year, extremes of temperature, restraint, starvation, suppressed sexual appetite, age, sex, and race are to be regarded neither as direct nor predisposing causes.

It is now universally accepted that the poison is communicated almost invariably by means of the bite of a rabid or infected animal.

Nothing is known of the specific infecting principle of rabies. The virus is contained in the saliva and foam of the diseased animal, also in the spinal cord, blood, and salivary glands; its existence in other portions of the body is conjectured but not positively determined. Neither by chemical or microscopic analysis of the saliva of rabid dogs has this virus been detected.

It increases by internal growth, and from other poisons it is distinguished principally by this circumstance, that it remains within the vital organism for weeks and even months without producing any diseased symptoms whatever.

In what manner, or by what course the specific poison penetrates the body from the wound is unknown, neither has its action while within the system been adequately explained.

Two theories have been advanced; either the virus remains awhile concealed and inactive at the seat of the wound or point of inoculation, and only after a certain interval - at the expiration of the period of incubation - enters and circulates with the blood and other fluids of the body; or else the poison, by undergoing inoessant reproduction, is constantly supplied in fresh quantities to the blood.

Virchow has compared the action of the poison to that of a ferment. fresh particles of which are constantly being conveyed into the blood from the seat of the inoculation, producing through the medium of the circulation the specific effect upon the nervous system.

Experiments have proved that the bite of an infected - though apparently healthy - dog, when inflicted during the period of incubation, or slow development of the disease, has even then the power of communicating it. Thamhayn collated nineteen cases, occurring in the human subject, in which dogs, to all appearances healthy, but which subsequently became rabid, produced by their bite hydrophobia, the result being fatal in eighteen cases.

The virus is probably capable of infection for some time after death but hardly longer than twenty-four hours. That the same is inactive when brought in contact with the unbroken mucous membrane of the digestive canal, is confirmed by the experiments of Hertwig; at one time he introduced the saliva and mucus of a rabid dog into the mouths and throats of healthy animals; again he fed dogs on food with which not only the infected saliva and mucus had been mixed, but to which also warm blood taken from rabid animals had been added, all with negative results. He placed healthy dogs in stalls where others affected with rabies had Just previously been kept, so that they were brought in frequent contact with the same straw, chains, food, and drinking basins that had been used by the diseased animals, but in no instance was rabies produced; and the same may be said of placing healthy animals in the stall with dogs which had recently died of the disease.

It is an acknowledged fact, demonstrated by numerous experiments that the milk and flesh of rabid animals (dogs, sheep, cattle) may, as a rule be consumed by man and animals without any ill effect, The theory that the poison is very rarely communicated in any other way than by the bite of a rabid animal, is fully confirmed by the most wearisome experiments. No instance is as yet known where the virus has been transferred by intermediate vehicles. An ingenious theory has been suggested, that if minute particles of the poison suffice to propagate infection, possibly certain 'parasites, fleas, lice, which are nourished by the blood of the dog, and which the more often infest them, may transfer the poison by means of their blood-drawing apparatus, and thus produce inoculation. It is inferred that an analogy exists with other infectious diseases, as for instance small-pox which has been unquestionably transported by flies, and the same is true in cases of malignant pustule. In the latter contagious and very fatal malady, it is believed that flies which have alighted on the ulcers of diseased animals convey the virus, and infect other animals and human beings.

Little or nothing is known as to a predisposition of rabies, it being estimated that less than two-thirds of the animals inoculated or bitten are infected by the disease. According to the experiments of some, a rich feeding of the dogs that had been inoculated, favored the outbreak of the disease, while on the other hand it was retarded by poor nourishment. Many dogs have resisted an infection; in three years Hertwig made nine attempts to inoculate his famous poodle. Some have been known to have been bitten four times by rabid animals and still remain unaffected, as in the case of a dog in the veterinary school at Lyons.