Hydrophobia (Gr. hydōr, 'water,' and phobos, 'fear') is a symptom of a disease known as Rabies, which may occur in man and in various animals; but the word hydrophobia is also frequently used to denote the disease itself. It has long been known that rabies is communicated from one animal to another if the saliva of the one is introduced into the organism of the second; whether it be the case that the first has bit the second, or has only licked it on an open sore. The saliva of a rabid animal produces no injurious effect if brought in contact with the unbroken skin of an animal, or even with a mucous surface, provided it be not excoriated. The dog is the animal most frequently affected by rabies.
When a rabid dog bites another animal the latter shows no immediate symptoms of disease. The wound caused by the teeth of the dog behaves like an ordinary wound and becomes cicatrised in the same manner. After the lapse of a certain period, which may vary from nine or ten days to several months (cases are known where the time has been as long as twenty-six or twenty-eight months), but is generally from four to six weeks, the animal that was bitten exhibits special symptoms; rabies has declared itself. The time that has lapsed since the bite was received is called the period of incubation. When the affected animal is a man, the first symptom is usually a change of character; he becomes melancholy and distrustful. Next, generally at the beginning of the case, appears a symptom called aërophobia—the smallest breath of wind which touches the skin of the face causes its muscles to contract. Next comes hydrophobia—if the sufferer is offered anything to drink, his throat contracts, and he suffers spasms of the pharynx. When this symptom appears the death of the sufferer is at hand, and is certain to occur in two or three days. During the interval between the appearance of the hydrophobic symptoms and death the patient has periods of calm and accesses of fury, and also exhibits paralytic symptoms which usually commence in the lower limbs.
Rabies is therefore communicated by biting from one animal to another; any scratch made by the teeth of the affected animal is harmless unless the saliva is conveyed to the wound. The animals liable to be affected by rabies are very numerous, and comprise almost all the mammalia—men, dogs, cats, horses, cattle, sheep, wolves, foxes, deer, &c.
The question of the etiology of rabies has remained very obscure until a very recent date; the most contradictory opinions were current when M. Pasteur in 1880 set himself to study this malady. His labours justify the following statements.
Rabies is a virulent disease, transmissible from one animal to another by the inoculation into the latter of those various secretions and tissues of the affected animal in which the virus dwells. This virus consists of a living organism which has not yet been made visible, by reason of the insufficiency of microscopic apparatus, but its existence can nevertheless not be denied. This statement, taken in connection with the results of M. Pasteur's labours in regard to the impossibility of Spontaneous Generation (q.v.), utterly contradicts the assertions of those who pretend to have observed rabies in animals which have never come into contact with rabid animals. Such assertions are always based on incomplete observations. If rabies could arise spontaneously in dogs, how can we explain the fact that vast regions like Australia may be wholly exempt from this scourge in spite of the great number of dogs there? The reason is that in these countries they most energetically prevent the introduction of any dog that can be suspected of rabies. If there were conditions under which rabies might spontaneously appear in dogs, then in territories so vast as the Australian colonies these conditions would certainly be realised from time to time. But there is no rabies in Australia.
M. Pasteur has studied the distribution of the virus in the individuals affected. He has observed that the virus was found in the nervous system and in the saliva, but not in the blood, the lymph, &c. Hence, if we inoculate another animal with the blood of a rabid beast, the first will remain wholly free of any rabid infection. Similarly, rabid virus introduced directly into the circulatory system of an animal will not produce rabies. But there is a sure means of communicating rabies from one animal to another—viz. by the introduction under the dura mater, on the surface of the brain, of a liquid which has first been sterilised and in which thereafter there has been soaked a portion of the central nervous system of the rabid animal. By this operation one is absolutely certain to communicate rabies unless the animal is refractory to rabies and cannot take the disease. In the course of his studies M. Pasteur observed that, in certain groups of animals which had been inoculated beneath the skin with large quantities of rabic virus, some not only did not take rabies, but became incapable of taking it—i.e. they might with impunity be inoculated on the surface of the brain with rabic virus. This observation was the origin of the discovery of preventive inoculation—of inoculation which renders an animal refractory to rabies.
The principle of such inoculation is as follows: The spinal cord of a rabbit which has died of rabies, when extracted from the body of the creature, and preserved in dry air at a constant temperature of 23° to 24° C. (74° to 76° F.), loses by slow degrees its virulence. With a spinal cord which has been so preserved for fourteen days it is impossible to communicate rabies to a rabbit or a dog. But this spinal cord has nevertheless still a certain power to confer immunity from the disease—the inoculation of an animal with a sufficient quantity of it will render it refractory to rabies. At the same time M. Pasteur observed that the freshest spinal marrows, that is to say, the most virulent, are those best fitted to confer immunity from infection. To render an animal refractory to infection the treatment commences by inoculating it with spinal cord fourteen days old, then with that of thirteen days, and so on till spinal matter three days old is reached, two days, one day, and even such as is not yet one day old. The last may be introduced into the subject of experiment without danger, because it is already refractory.
What gives this discovery an enormous value is that these preventive inoculations made on an animal early enough and swiftly enough after it has been bitten prevent rabies from declaring itself. This is explicable on the following grounds: The virus is deposited by the dog's bite in a superficial wound; there it meets with little nerve-filaments in which it is further cultivated, and by means of which it ascends, somewhat slowly, to the nervous centres. These nerve-centres are the quicker affected the nearer to them the bite has been inflicted: hence bites on the head produce rabies after a shorter period of incubation than bites on the extremities of the body. If there is time to render the organism refractory by means of the preventive inoculations before the nerve-centres are affected the victim is saved; the nerve-centres once affected and destroyed, it is evident that no power of man can bring about a cure.
What ought to be done when any one is bitten by a mad dog is this. The wound made by the dog's teeth should be cauterised as soon as possible, and deeply too, so that if possible the virus may be destroyed before it has begun to cultivate itself in the nervous system. Then, if it is certain that the animal which inflicted the bite is mad, or if there is good reason so to believe, the victim should be sent as speedily as practicable to the nearest 'Anti-rabic Institute.' It is obvious that his safety depends on the quickness with which this is done. It is also obvious that bites on the head are more serious than bites on the limbs, inasmuch as there is a shorter distance to be traversed ere the nerve-centres are reached.
How can one make sure that the biting dog is mad? If possible the dog should be kept under observation without being killed; for it is much easier to recognise rabies in a living animal than by the earliest post-mortem examination. The animal will change its character, will often cease to eat, will bite everything within its reach, and will sometimes show signs of paralysis, its hind-quarters and its lower jaw being first attacked. In such cases the animal will inevitably die in from three to four days, or at most in eight days. A post-mortem examination will show the stomach empty of food, and containing on the contrary foreign substances such as bits of wood, stones, straw, &c. The most certain way of discovering if a dog was really mad is to introduce by way of inoculation a portion of its medulla under the dura mater of a rabbit. The rabbit will inevitably become rabid if the dog was rabid, but this will not take place till after fifteen or eighteen days; so that it would be imprudent for a person who had been bitten to await the result of the experiment before beginning to undergo preventive inoculation.
Statistics of the proportion of deaths by hydrophobia had never been properly kept up to the time of M. Pasteur's work in this department. Few doctors actually knew this terrible malady. It is generally said that of a hundred persons bitten by mad dogs some nineteen or twenty die of hydrophobia. This figure is probably too low. The mortality amongst cases treated at the Pasteur Institute (established by him in Paris in 1886) has fallen to less than per cent.
[So far M. Pasteur has sketched his discoveries and practice in regard to rabies, but a brief unargumentative review of current adverse criticism is also requisite. (1) As a working hypothesis, Pasteur assumes the occurrence of a specific microbe of rabies, which (in spite of various sanguine in- vestigators) has not yet been demonstrated. In default of this demonstration, it seems to many that both the practice and the theory of rabie inoculation lack security and conclusiveness. (2) Again, there are some who, while believing vaccination to be empirically justified, are dissatisfied with the warrant for the anti-rabic treatment. They urge the acknowledged divergence between the two methods, and criticise the principle on which Pasteur works. (3) As to the warrant furnished by Pasteur's results, it is argued that the statistics are unreliable—e.g. because many of the patients inoculated were probably never infected, because in genuine cases the prevention may have been due to preliminary cauterising and to factors apart from the anti-rabic inoculation, and for various other reasons which forcibly suggest that in drawing inferences from statistics the sources of error are indeed numerous. (4) Less useful criticism is that which emphasises what is often true of progressive medical investigation—namely, that there have been failures in Pasteur's treatment, that certain tentative measures were confessedly futile, that there have been striking changes of method, and so on. (5) More serious is the allegation that some deaths have occurred as the result of the inoculations rather than of the infection from the rabid animal. Of such not altogether unprecedented casualties the possibility, but not the actual occurrence, was admitted by the English Investigation Committee (1887), while Dr Armand Ruffer, who speaks with much authority, denies (1889) with all deliberateness that there is any case on record in which it can be proved that death has followed as the result of Pasteur's treatment. (6) The anti-vivisectionists have urged against certain implications of Pasteur's procedure various considerations which merit careful discussion, though without special bearing on the present problem. (7) So, too, the thorough-going anti-vaccinationists are of course among the critics of Pasteur, but their arguments can best be dealt with in connection with vaccine inoculation, about which we know at least a little more than we do in regard to the anti-rabic preventive (see VACCINATION). (8) Though there is much to be said on both sides, those who are willing to leave the problem to the experts will believe meantime that Sir James Paget, T. Lauder Brunton, George Fleming, Sir Joseph Lister, Richard Quain, Sir Henry E. Roscoe, J. Burdon Sanderson, and Victor Horsley had good reasons for saying in the Report which they presented to parliament in 1887: 'It may, hence, be deemed certain that M. Pasteur has discovered a method of protection from rabies comparable with that which vaccination affords against infection from smallpox.'
In 1889 a Mansion House Fund was raised in London to enable poor English sufferers to be taken to the Institute; but like every other recognition of Pasteur's method, the scheme was reviewed with keen hostility by anti-vivisectionists and anti-vaccinators. In 1890 Dr Paul Gibier, a pupil and assistant of M. Pasteur, opened a Pasteur Institute in New York.
See Report of a Committee on M. Pasteur's Treatment of Hydrophobia, presented to parliament, 1887. For good summaries of Pasteur's method, see Dr E. Roux, Croonian Lecture, Proc. Roy. Soc. xvi. (May 1889); Dr A. Ruffer, Brit. Med. Jour. (September 1889); Vignal, Brit. Med. Jour. (April, May, 1886). See also papers by Pasteur in Comptes Rendus Acad. Paris, in Bulletin de l'Acad. de Méd. (from 1881 onwards), in the Annales de l'Institut Pasteur, and in the New Review (November 1889). See also Louis Pasteur, his Life and Labours, by his son-in-law (trans. by Lady Claud Hamilton, Lond. 1885). Of works published before Pasteur's discoveries, it must suffice to mention that of Fleming. For criticisms of Pasteur, reference may be made to publications of the Anti-Vivisection societies (especially Victoria Street, London), to papers by Dr A. Lutaud in the Jour. de Médecine de Paris; Dr T. M. Dolan, M. Pasteur and his Methods: a Critical Analysis (Lond. 1886); Dr C. W. Dulles, Medical Record (New York, 1886); Dr M. Biggs, The Medical News (Philadelphia, 1886)].