Rabies and Hydrophobia

BY JAMES LAW, F.R.C.V.S.

SYNONYMS.—Canine Madness, Rabidus Canis, Canis Rabiosa. Greek, Lyssa, Lytta, Lyssa Canina, Cynolyssa, Hydrophobia, Pantephobia, Ærophobia, Phobodipsia, Erethismus Hydrophobia, Clonos Hydrophobia, Dyscataposis. French, Tetanus Rabien, La Rage, Toxicose Rabique. German, Wuth, Hundswuth, Tollwuth, Wuthkrankheit, Hundtollheit. Italian, Rabbia, Arabiata. Spanish, Rabia, Rabiosa. Swedish, Hundsjuka. Roumanian, Turbarea.

DEFINITION.—Canine madness is an acute infectious disease, supposed to arise spontaneously in the genus Canis (dog, wolf, fox, etc.) and Felis (cat, etc.), but transmissible by inoculation to the other Mammalia and to birds. It is characterized by a long period of incubation, by exaggerated reflex excitability, by disorder of the intellectual, emotional, and other nervous functions, by change of habits, by extreme irritability of temper, by optical and other delusions, by spasms of the muscles of the eyeballs and throat, by paralysis, and by more or less fever. The disease runs a short and almost without exception fatal course.

HISTORY.—Plutarch claims that hydrophobia was first recognized by the Asclepiadæ, and Homer's allusions to the malign dog-star and to Hector's acting like a raging dog have been quoted as implying a knowledge of rabies. We find no certain reference to the affection, however, until we come to Democritus and Aristotle, in the fourth century B.C. The latter clearly describes the disease and uses the name lytta, but, singularly enough, claims for man an exemption from the general susceptibility to the infection by inoculation. From that date to this the successive outbreaks, sufficiently noteworthy to secure a place in history, are so numerous and widespread as to show a continuous prevalence of the malady in the Old World, and, since the early part of the eighteenth century, in the New.

Historia Animalium, lib. viii. cap. 22.

GEOGRAPHICAL DISTRIBUTION.—Rabies is more prevalent in temperate regions than in the tropics and Arctic Circle, but this is common to all animal plagues propagated solely or mainly by contagion, and is manifestly due chiefly to the density of population, the activity of commerce, and the free movement of men and animals in the temperate zone. That a hot or cold climate is incompatible with rabies is disproved by its prevalence under the tropics in Southern China, India, Abyssinia, the West Indies, Peru, Chili, and Brazil, and in the Arctic Circle in Northern Greenland, Lapland, Siberia, and Kamtchatka. On the other hand, many islands and secluded regions in the temperate zones maintain a continued immunity or have been invaded only recently by the introduction of infected dogs. We may instance the Hebrides, Australia, Tasmania, New Zealand, South Africa, West Africa, the Azores, St. Helena, and, until the last half century, La Plata, Malta, and Hong-Kong. The disease is well known throughout North Africa, Arabia, Syria, Turkey, and Asia generally, in Ceylon and other of the East Indian islands. It is also notorious that even when unusually prevalent its progress is often abruptly arrested by a considerable river, and Schrader and Virchow both notice that though it ravaged both banks of a river, yet the islands in the river escaped, as was notorious of the islands in the Elbe during the great Hamburg epizoötic in 1852-53. While, therefore, rabies prevails most extensively in the more civilized countries and in large cities, yet we can point to no geographical area in which the contagion has failed to spread among those bitten by rabid animals, nor to any locality in which the disease has been shown to arise spontaneously from unwholesome conditions of climate, soil, or general environment.

ETIOLOGY.—We know of but one efficient cause of rabies—namely, infection. Yet as many conditions are believed to favor its extension, or even to determine its spontaneous eruption, it is necessary to speak of them shortly.

As shown above, climate cannot be charged with the generation nor diffusion of rabies. Many countries formerly thought exempt are now known to suffer. The following may be named: The East and West Indies, Syria, Egypt, Cyprus, Siberia, the lands north of the Baltic, and South America. Others manifestly maintain their exemption only because the morbid germ has not yet been introduced.

Certain seasons undeniably show a far wider extension of the disease than others, but such epizoötics are not limited to a particular season or year, and, unless cut short by human intervention, cover a succession of years of the most varied climatic character, spare inaccessible or secluded islands in the very centre of the outbreak, and the cycles of prevalence will succeed each other, in place of occurring simultaneously, in closely adjacent countries subject to the same climatic vicissitudes, but separated by narrow seas. Even a broad river destitute of bridges usually abruptly arrests an epizoötic, and protects the land beyond lying under precisely the same general influences. In this connection may be quoted the recent great epizoötic of 1856-72 in England, which succeeded, but did not accompany, that of 1851-56 in Germany. Prof. Röll reports the extraordinary prevalence of rabies at Vienna in 1814, 1815, 1830, 1838, 1842, and 1862—years remarkable for diversity rather than uniformity of climatic characters.

Popular opinion refers rabies to the extreme heats of summer, and each year dogs are muzzled or otherwise confined by order of municipal authorities during the dog days, though left at liberty throughout the rest of the year. In 1780, Andry observed that the coldest and hottest months furnished the least number of cases, and later Hurtrel D'Arboval claimed that in France dogs suffered most in May and September, and wolves in March and April. Bouley claims that the majority of dogs suffer in March, April, and May. The following statistics are interesting in this connection:

Cases of Rabies in

WINTER. SPRING. SUMMER. AUTUMN.

Dec., Jan., Feb. March, April, May. June, July, Aug. Sept., Oct., Nov.

Dogs 755 857 788 696 (Bouley).

Men 17 25 42 13 (Boudin).

The increase of cases of rabies canina in the spring and summer months, as shown by the above statistics (7-15 per cent.), cannot reasonably be attributed to the influence of the weather, since even the strongest advocates for spontaneity would at once decline to claim any such ratio of spontaneous developments. The increase must therefore be mainly, if not altogether, due to the increased number of inoculations; and these latter are provided for in the jealousies and quarrels in the troops of males that follow each rutting bitch in spring, the principal period of oestrum in the canine female. The infection spread in this way in early spring tends to remain more prevalent throughout the hot summer months.

With regard to the greatly enhanced mortality in man during the summer months, as shown in Boudin's statistics for France, in the absence of any genuine hydrophobia in man apart from inoculation from a rabid animal, it may be attributed to three principal causes: 1st. The bites sustained from rabid dogs in spring and early summer, when the disease is most widely spread among these animals, will give rise to hydrophobia weeks or months later. 2d. In the warm season the body is more thinly clad and the hands and other portions are more frequently left bare, so that the teeth are less likely to be cleansed of the virulent saliva by passing through the clothes before entering the skin. 3d. The languor, fever, and nervousness attendant on extreme heat tend not only to hasten the activity of any disease-germs actually present in the system, but also strongly favor the increase of that nervous fear which so often generates a fatal pseudo-hydrophobia (lyssophobia) in persons that have been bitten by dogs.

Hunger, thirst, and spoiled food are invoked as causes of rabies, yet in the East, where the dogs are the scavengers of the cities and often suffer severely from hunger and thirst, eat the most offensive carrion, and drink the foulest water, the disease has a very restricted prevalence, while in South Africa and Australia the outcast and sheep-dogs, often the victims of starvation and thirst, entirely escape. Bourgelat, Dupuytren, Majendie, Breschet, and others have cruelly destroyed dogs by privation of food and water and by exposure under a broiling sun, but no rabies, nor anything resembling it, was produced. Dogs perspire little and suffer severely from heat, but there is no evidence that this can develop canine madness. It is claimed that Rossi of Turin developed rabies in cats by withholding food and drink, but, as he furnishes no inoculation-tests confirmatory of its virulence, the claim cannot be endorsed. Experiments with an exclusive diet of salt meat, putrid meat, and water only have failed to produce rabies.

The large preponderance of male dogs attacked with rabies has been constantly remarked by writers. Of 1990 rabid dogs reported by different authors, 1746 were males and 244 females—a ratio of more than 7 to 1. This excess of males attacked is much higher than the ratio of males in the dogs of the districts drawn upon. Thus, Bourrel found a ratio of 6 rabid males to 1 rabid female, while in his patients generally the proportion was 4 to 1. Leblanc found that 14 per cent. of the male dogs went mad, while but 1 per cent. of the females suffered. That sex is no protection against inoculated virus is shown by the frequent inoculation of castrated dogs of both sexes. The excess of male subjects may be attributed mainly to the frequency with which these bite each other when following a female in heat, and the respect of all alike for the latter sex. Even in the rabid dog the sexual instinct rises above the propensity to bite in the early stages of the malady.

Toffoli claims that he has caused spontaneous rabies by shutting up several dogs in a loose box with a bitch in heat and allowing them to fight for the prize. Weber and Leblanc have noticed similar occurrences. But Greve and Menecier have repeated the experiments with a contrary result; so that it remains probable that when successful the victims had already been inoculated before they were shut up. Moreover, the seclusion of male canine animals for a lifetime in menagerie cages, often adjoining those of their corresponding females, has never been known to induce rabies.

The bite of the violently enraged dog, and the bites mutually given when following a rutting bitch, are popularly supposed to cause rabies; but if this were the case, the disease must have been universally prevalent. The idea that the bite of a dog will cause hydrophobia should that dog at any subsequent period go mad is a similar delusion. Men doubtless occasionally develop lyssophobia under such an influence, but animals do not contract genuine rabies.

Dogs are alleged to have gone mad from violent suffering after an operation, and cats from being scalded or robbed of their kittens, but all such causes are continually operating without such effect, and when in a solitary case rabies develops, it can only be looked on as a coincidence.

Much popular prejudice exists against certain breeds, and the Pomeranian has been virtually ostracised on account of its supposed liability to rabies; but statistics show that the liability to contract the affection bears a relation to the exposure rather than the special breed. Eckel, Pillwax, and Hertwig found that dogs kept as house- or watch-dogs, and most pampered and confined, are the most liable, while St. Cyr and Peuch found the greatest number of cases among those running at large and allowed the freest exercise.

There is a popular belief that the bite of the skunk (Mephitis mephitica) is always rabific. Rev. H. C. Hovey describes a number of cases of infection from this animal, and John G. Janeway has reported other instances. Both claim that the disease is spontaneous in the skunk, and Mr. Hovey holds, on very insufficient grounds, that the affection is a distinct variety of rabies (rabies mephitica). The facts seem to warrant only the conclusion that skunks in certain districts of Michigan and Kansas have had rabies communicated to them, and follow the rabid impulse to bite other animals and men. The Mephitinæ abound in the Eastern States, but we never hear of them stealing up and biting men or dogs, nor of the latter contracting rabies from skunk-bite. Eastern dogs frequently kill skunks and sustain bites, but do not thereby contract rabies. Even in Kansas this evil influence of the skunk-bite was unknown until 1870, showing that it is not inherent in the climate nor soil, but has been presumably imported. The spontaneity of the affection is assumed, not proved.

Amer. Jour. of Science and Art, May, 1874.

New York Medical Record, March 13, 1875.

In the above epitome of alleged causes we find nothing proving the spontaneous evolution of rabies. The prevalence of the affection in wolves, foxes, jackals, cats, skunks, etc. proves nothing for spontaneity, more than its existence in the dog. In all these species of animals the malady develops the dread propensity to bite, and thus in all alike provision is made for the perpetuation and propagation of the malady. Unless a previous attack by a rabid animal has been observed, owners usually insist that their dogs have contracted the malady spontaneously, yet a rigid scrutiny will almost always reveal a strong probability, at least, of inoculation. The rabid dog wanders far from home, and sometimes accomplishes wonderful feats of leaping to reach his victim, so that his presence in a district is not even suspected, and animals thought to be safely secluded inside high walls suffer from his fangs. He is more inclined to bite and rush on than to stay and devour, and thus small animals, like the skunk, when bitten may survive to propagate the disease in places to which a dog could not possibly find access. Much circumstantial evidence makes strongly against the theory of spontaneity. Thus, the immunity of the islands of the Elbe in the very midst of a severe and protracted epizoötic, the continued immunity of the Hebrides and of Malta, each famed for its indigenous race of dogs, for long centuries, during which the malady prevailed at frequent intervals on the adjacent mainlands, and the continued exemption of South Africa and of the Australasian and other islands, in the face of the counter-fact that the affection persisted after importation in the West Indies and South America, speak strongly for the doctrine that the introduction of a pre-existing germ is an essential condition of the evolution of the disease. The following statistics of cases which entered the Berlin Veterinary College furnish further corroborative evidence. There entered the college,

In 9 years, 1845-53, inclusive, 278 rabid dogs.

In 1854, 4 rabid dogs.

In 1855, 1 rabid dog.

In 1856, 1 rabid dog.

In 5 years, 1857-61, inclusive, 0 rabid dog.

The average for each of the first nine years was a fraction less than 31. In the two last of the nine the cases rose to 68 and 82, and this led early in 1854 to an order for the muzzling of all dogs, which was rigidly enforced by the police. The disease was promptly suppressed, the two cases in the two succeeding years being probably due to infected kennels or to importation from without. The results in Eldena (Fuertenberg) and Holland (Van Capelle) are equally conclusive. The inefficiency of some orders for the muzzling of dogs makes nothing against these facts. A law on the statute-book is not always a law in force, as I saw in Alfort and Lyons in 1863; the dogs wore their muzzles only in honor of the periodic visits of the commissionnaire of police, and rabies prevailed.

The great majority of competent observers of to-day deny, or at least strongly doubt, the occurrence of the disease apart from inoculation. Without assuming to decide the question for all times and places, it may be safely asserted that there is no sufficient proof of such an occurrence in any recent time.

Mr. Sâzé, a former student, informed me that boys in Japan produce what is believed to be canine rabies by administering to dogs a fungus (bukeryo) found growing on a coniferous tree. The dogs do not all seem to die, but are usually killed by way of precaution. The symptoms are those of delirium, with a propensity to bite, and the disease is assumed to be communicable, though no facts are given to show that it is so. This popular fancy has all the air of a popular fallacy, but as the counterfeit attests the genuine, it shows the familiarity of the Japanese with true rabies.

The contagion of rabies is usually resident in the saliva, but is by no means confined to that product. Paul Bert found the bronchial mucus virulent in dogs in which the saliva was non-virulent. The flesh has conveyed the disease when eaten, though probably only because of sores or abrasions on the alimentary tract. Smith records the death of negroes in Peru from eating rabid cows; Schenkius, that of persons who ate of a rabid pig; and Gohier and Lafosse have infected dogs by feeding the flesh of rabid dogs and ruminants; Rossi and Hertwig have separately induced rabies by inoculating sound animals with portions of nerves from rabid ones. No absolute proof can be adduced that the disease has been conveyed through consumption of the milk. Cases quoted to show its virulence are open to the objection that the dam probably licked the offspring. A similar uncertainty attaches to the spermatic fluid. Women are alleged to have acquired hydrophobia by coitus, but no such case can be adduced among animals, though rabid males have often had connection with healthy females. The alleged cases in women were therefore probably the result of an excited imagination or caused by virus introduced through some other channel. The breath and perspiration seem incapable of becoming media for the transmission of the disease. The blood was supposed to be non-virulent by Breschet, Majendie, Dupuytren, Blaine, Youatt, etc., but has been shown by Eckel and Lafosse to be rabific. Eckel successfully inoculated the blood of a rabid he-goat on a sheep and that of a rabid man on a dog. Lafosse accomplished the same in one of three attempts by inoculation from dog to dog. The blood is probably only virulent in the advanced stages of the disease, and its virulence implies the virulence of all vascular tissues.

Peru as it Is.

The saliva of rabid Herbivora and Omnivora, long held to be harmless, is now known to be virulent. Berndt has successfully inoculated it from an ox to four sheep; Eckel from a goat to a sheep; Rey from sheep to sheep; Lessona from an ox to two horses and a sheep; Tombaro from a heifer to a sheep, a horse, and two dogs; Youatt from horse and ox respectively to dogs; Ashburner from an ox to fowls; King from a cow to fowls; and Majendie, Breschet, Eckel, Hertwig, and Renault from man to dog; and Earle from man to rabbits. Besides these are a series of accidental cases, as from horse to man (Youatt), from a sheep to its shepherd (Tardieu), and from man to man (Aurelianus, Enaux, Chaussier).

Experiments by Hertwig and Eckel seem to show that saliva loses its virulence on the supervention of cadaveric rigidity or putrefaction in the dead body. Haubner even believed dried saliva to be innocuous. Yet Count Salm successfully inoculated the dried saliva of a rabid dog, and Schenkius reports a case of hydrophobia produced by a scratch of a hunting-knife that had been used to kill a mad dog some years before. A veterinary student at Copenhagen cut his finger while dissecting the body of a rabid dog twelve hours after death, and died of hydrophobia six weeks later. These cases in man may, it is true, have resulted from fear, but the same cannot be said of the infection of hound after hound placed in empty infected kennels, as recorded by Blaine, Youatt, and others. In the face of this it would require very strong negative testimony, indeed, to prove that the virus of rabies is devitalized in drying—a process which prolongs the vitality of other virulent matters.

Up to the present time the germ of rabies has not been demonstrated. That it is a particulate living organism may be reasonably deduced from its power of indefinite increase—a quality possessed by no mere chemical nor mechanical agent, also from the saliva proving non-virulent after filtration through plaster, while the solid residue left on the filter was virulent (Bert). But, although bacteria have been found in the saliva, those demonstrated up to the present are manifestly ordinary aërial bacteria, such as in Pasteur's experiments produced septicæmia rather than rabies. It still remains, therefore, for some future observer to discover that germ of which we cannot doubt the existence.

The point of election of this germ appears to be mainly the nervous tissue. Pasteur found the brain-matter of rabid animals invariably infectious, and has preserved the moist brain in an infecting condition for three weeks at a temperature of 12° C. He found that by direct inoculation in the brain-substance the period of incubation was abridged, rabies often showing itself in six, eight, or ten days. In the face of Rossi's successful inoculation of nerves and Pasteur's results with brain-matter it is difficult to account for the unsuccessful inoculation of nerve-tissue in six successive experiments by Hertwig. It seems to show that though the virus is concentrated in the brain, and especially in the medulla and pons, yet it does not equally permeate the entire nervous system. This election of the poison for the nervous tissue led Dr. Douboue in 1851 to advance the theory that it is propagated from the seat of inoculation to the brain through the medium of the nerves—a position now assumed by Pasteur. This, we fear, is not well founded. The poison, advancing for a month or more along the lines of the nerves, would probably derange and abolish their functions, as it does so speedily and effectually that of the nerve-centres after it has gained a seat in them, whereas, in reality, the local paralysis only appears in the last stages and after the symptoms of cerebral disorder are well established. Furthermore, a common premonitory symptom of rabies is congestion, swelling, and irritation of the inoculation wound, showing a sudden extraordinary activity at that point as a herald, if not a condition, of the general infection, whereas under a slow propagation along the nerves from the first this irritation would probably have been greatest in the wound at the outset, and would have thereafter kept pace with the progress of the virus along the nerves. Again, the blood is not always infecting. Blaine, Youatt, and others of the older observers had no fear of the blood. Hertwig obtained rabies in two cases only out of eleven inoculations with the blood of rabid subjects. The blood in this, as in some other diseases (variola equina, v. ovina, lung plague of cattle), proves to a certain extent inimical and destructive to the poison. Galtier inoculated nine sheep and one goat by intravenous injection of the saliva of mad dogs, in no case with fatal results nor indeed with any manifestation of rabies, but with the effect of fortifying the system so, that subsequent inoculation into the tissues of the saliva of rabid animals was harmless. Test inoculations made in the tissues of other animals with the same virus used in his intravenous injections, and his subsequent inoculations of the animals so treated, invariably determined rabies. Pasteur repeated these intravenous injections in dogs with the result of rapidly inducing rabies in a fair proportion of cases. One of his cases produced in this way recovered, and thenceforward resisted all further inoculation with the virus. Others that did not perish from intravenous injection afterward died of rabies after inoculation in the brain. Unfortunately, neither Galtier nor Pasteur have reported how much virulent saliva was injected in any one case, so that we have no data as to whether the difference was due to the varying quantity of the virus introduced in the various cases. Lussana, an Italian physician, had already in 1878 experimented on two dogs by injecting into their veins the blood of a physician who died of hydrophobia. The blood was drawn by leeches and cupping-glasses, and five grammes were injected into each dog. One died on the twenty-fourth day, presenting the symptoms and post-mortem appearances of rabies. The second at the end of one hundred and forty days developed symptoms of rabies which lasted a month, when the animal was sacrificed, and nothing special found at the autopsy. The data do not warrant a very positive conclusion, yet they seem to imply that the receptivity on the part of the dog is greater than that of the small ruminants. They suggest, further, a greater relative potency in the battle for life of the blood-globules of the small ruminants with this unknown rabific germ. This antagonism between the blood of the ruminant and the germ of rabies finds a parallel in the case of other disease-poisons in their relations to the nuclei of the tissues. Thus animals may prove refractory to a small dose of the poison of anthrax, yet Chauveau has shown that this virus will overcome all native or acquired insusceptibility when administered in excess. The same is true of the poison of chicken cholera, which Salmon dilutes until it is non-fatal, though still affecting the system and conferring an immunity from its attacks in the future. So with the lymph of variola ovina, which Peuch diluted to 1/50 and injected with the effect of producing slight fever and immunity without vesiculation.

This view would imply that in ordinary cases (inoculation with a moderate amount of the poison) the virus is for a time localized in the vicinity of the wound; and this is further supported by the fact that thorough excision and cauterization of the wound some time after it has been received is still often protective. It is weakened by the fact that bites of dogs in the stage of incubation sometimes produce rabies, but it must be borne in mind that there is still a period between the passage of the living germ to the salivary glands and brain and the growth of the germ in the nerve-centres, so as to produce pathognomonic symptoms, during which both blood and saliva must be virulent.

The ratio of successful inoculations to the bites is very varied. Thus, out of 555 dogs reported to have been bitten by rabid dogs, 188 contracted rabies; out of 183 experimentally exposed till bitten or inoculated, 91 became mad; out of 73 cattle bitten, 45 became rabid; out of 121 sheep bitten, 51 succumbed; and of 890 persons bitten, 428 took hydrophobia (48 per cent.). Of 440 bitten by rabid wolves, 291, or 66 per cent., took the disease. Such statistics are, however, far from satisfactory. Of dogs reported mad, some have only suffered from epilepsy, convulsions, or colic, while of those bitten by the really mad dog, some have sustained simple bruises without any real abrasion; in other cases the teeth have been wiped clean by passing through thick wool, hair, or clothing, or even the flesh of other animals just bitten; in other cases the bite has been inflicted at a time when the virulence of the saliva was at its minimum, or in a subject which was naturally insusceptible. The protective effect of clothing was well illustrated in a case which came under my notice in London. Six animals bitten by a rabid dog all contracted rabies, whilst a man bitten a few hours before through the coat-sleeve, and who did not have the wound cauterized for a full hour after the bite, escaped. Bouley found that in 32 persons bitten in the face, 29 died of rabies (90 per cent.); of 73 bitten on the hands, 46 died (63 per cent.); of 28 bitten on the arms, 8 died (28 per cent.); of 24 bitten on the lower limbs, 7 died (29 per cent.); of 19 bitten on the body (usually multiple wounds), 12 died (63 per cent.). The high mortality from the bites of rabid wolves and skunks is mainly due to this habit of attacking the face and hands. As illustrative of insusceptibility may be quoted the poodle of Hertwig, which was inoculated nine times with unquestionably rabic virus without effect; also the pointer of Rey, which was seventeen times bitten by rabid dogs without harm; also the acquired immunity of Galtier's sheep and rabbits, above referred to.

INCUBATION.—In the dog this varies from 6 days (Pasteur) to 240 days (Bollinger). In the majority of cases it ends in from 20 to 50 days. Pasteur, by inoculating into the brain substance direct, reduced the incubation from 20 days to 6 days. In the horse the limits of reported cases are from 15 days to 92 days. In the ox incubation varies from 20 to 30 days; in sheep, from 20 to 74 days; and in swine, from 20 to 49 days in recorded cases.

In man incubation is believed to be often much more prolonged. In 6 per cent. of all cases it is from 3 to 18 days; in 60 per cent., from 18 to 64 days; and in 34 per cent. it exceeds 64 days (Hamilton, Thamhayn). Quite frequently symptoms of hydrophobia appear from three to six months after the bite; in a few the period is prolonged to one or two years, and in rare instances to seven (Schule), and even twelve years (Chabert). But all such cases of prolonged incubation in man are at the least extremely doubtful. Man often contracts a pseudo-hydrophobia as the result of fear, and is curable by moral suasion alone; and as no such protracted incubations are noticed in the lower animals, and as no one of these abnormally deferred attacks in man has been verified by successful inoculation on animals, it is prudent to reserve a full assent until they are supported by better testimony. A specimen of such cases is that recorded by Chirac, in which a cadet bitten at Montpellier afterward spent ten years in Holland, and then, returning and hearing that his fellow-cadet bitten by the same dog had died of hydrophobia, he also manifested the disease and died. Another is the case of a man who, after having been bitten, spent two years in prison, and then developed hydrophobia and died. A mind naturally erratic and rendered weaker and more susceptible by prolonged confinement would prey upon itself and exaggerate the danger when the subject had been forcibly presented. In all such cases the attending physician should feel bound in the interests of humanity to inoculate a dog or other animal and ascertain whether or not the disease is virulent. The value of such results in dealing with future cases of the same kind cannot be overestimated.

The period of incubation appears to be relatively shorter in the young (average 45 days) than the old (average 70 days), and is believed to be shortened by constitutional excitement from violent passion, fever, the heat of the weather, or electrical disturbances.

During incubation no sign of the disease can be detected; it is even said that the wounds heal with unusual rapidity; but it is certain that toward the end of the latency the cicatrix, alike in man and animals, tends to become sensitive, itchy, congested, and even the seat of papular eruptions. The vesicles (lyssi) which, according to Xanthos, Marochetti, and Magistel, appear near the opening of the sublingual glands within a few days (6 to 20) after inoculation, have not been found by any recent observer.

SYMPTOMATOLOGY.—Three forms of rabies in the dog are recognized—the furious, the paralytic, and the lethargic. The prodromata are, however, the same in all, so that these may be conveniently considered before the different types are noticed.

The premonitory symptoms are by far the most important, as if these are recognized the dog may be safely secluded or destroyed before there is any disposition to bite. Any sudden change in a dog's habits or instincts is ground for suspicion. Bouley well says that a sick dog is always to be suspected. In some cases there is unusual dulness and apathy, in others great restlessness, watchfulness, and nervousness. A morbid appetite, in house-dogs a tendency to pick up and swallow straws, thread, paper, pins, and other objects, or to devour their own dung and urine, is highly characteristic. A desire to lick cold smooth objects, as a stone, a boot, a piece of metal, or the nose of another dog, is often seen. Smelling and licking the anus or generative organs of another dog and the exhibition of sexual desire are frequent manifestations. An increased fondness for the owner, shown by fawning and licking, is occasionally seen, though more commonly there is a change from a formerly amiable temper to a morose, sullen, retiring, and resentful disposition. If a naturally quiet dog flies into a violent passion at the sight of another dog or a cat, and attempts to bite it, he should be carefully watched. If a social dog seeks seclusion and darkness, or if while crouching and shrinking from a blow (hyperæsthesia) he yet bears it without howl or whine, he is to be strongly suspected. Barking without object, constant moving, searching, and scraping, a disposition to tear wood, clothing, etc. to pieces, and, above all, an absence from home for a day or two, should beget grave apprehensions. The rabid bark or howl which is often heard early in the disease is hoarse, low, and muffled, partaking of the nature of both bark and howl, the first running into the second, and consists of one loud howl followed by three or four others progressively diminished in force and uttered without closing the mouth. Some rub the chaps with the forepaws as if to dislodge an offending body from the mouth; others reject bloody matter by vomiting; and others turn the head and eyes as if following imaginary objects, and snap at them. Finally, a tendency to bite, rub, or gnaw the wound is significant, and usually draws attention to the fact that the wound, long healed, is still red, sensitive, and swollen, or even papular. The conjunctivæ are usually congested, there is an increased nasal defluxion, and the skin of the forehead and over the eyes is drawn into wrinkles. This stage lasts from a half to two or three days.

Following one or more of the above symptoms, paroxysms of wicked fury come on, alternating still with periods of quiet, in which prodromata only are observed. The red congested eyes assume a fixed stare, often squint or roll as if following an imaginary object, at which the dog presently snaps. A paroxysm is ushered in by increasing uneasiness, frequent change of position, and a desire to escape, shown in rushing at the door, tugging at the chain, or gnawing the post and walls of the kennel. The tendency to bite and gnaw is further shown by seizing the straw or tearing to pieces wooden and other articles within reach, or even by the victim lacerating its own body.

The rabid howl becomes more frequent, and the rage and disposition to bite strange animals and persons merge into a mischievous desire to worry all that come in the way, the respect for former companions and friends being steadily lost as the paroxysm increases in violence. Yet for a considerable time the voice of a loved master recalls the suffering animal to some degree of self-control. If free to escape during such paroxysms, the dog expends his excitement in wandering, making long journeys of five, ten, or twenty miles, and flying at every animal or man he meets, especially if they increase his excitement by any noise or outcry. If the victim escapes destruction during one of these wanderings, he returns during a lucid interval exceedingly dangerous, for, though he may recognize or even fawn upon his friends, yet the demon of mischief is even more potent within him, and may be roused to sudden violence by any noise or excitement. The intervals of quiet are attended by a prostration proportionate to the violence of the previous paroxysm, and the animal usually seeks seclusion and darkness, where he may lie dull and torpid, but he may be roused at any time to a renewed paroxysm by any noise, disturbance, the presentation of a stick, or, above all, by the approach of another animal. During the paroxysm the animal is manifestly the subject of acute delirium, has hallucinations, snatches and bites at unreal objects, turns on his best friends, even his master, seizes and holds on to a stick or iron bar until the teeth are detached and the gums lacerated, bites his own body, even amputating tail, testicles, or toes with his teeth; a bitch deserts her puppies or worries them, and all follow the unconquerable impulse to wander and to wound living beings. The victim will sometimes manifest incredible strength in breaking his chain and scaling high walls. Twitchings of the muscles of the face, and even general convulsions, are sometimes seen. Food is usually rejected, or if swallowed is soon vomited. In the course of two or three days the furious stage merges into the paralytic one, first shown by paresis of the hind extremities and a swaying motion in walking, then by paralysis of the lower jaw, which hangs pendent and allows the escape of a viscid saliva. The palsy gradually extends over the whole body—a sure precursor of approaching death, which is rarely delayed beyond eight days, and never more than ten, from the onset. In this last stage the animal has become extremely emaciated, with dry withered hair, hollow flanks, and small weak pulse; he may at first rise on his fore limbs when disturbed, and even attempt to snap, but there is now little danger of a bite. Convulsions may alternate with the paralysis. The result is invariably fatal.

The peculiarity of dumb or paralytic rabies in dogs is that the last or paralytic stage supervenes at once on the prodromata, without any intervening period of acute delirium and fury. The animal is throughout dull, quiet, and depressed, and shows little tendency to bite, to wander, or to restless movement. The excitement of the sexual passion is the same as in the furious forms, and the howl is still emitted, though much more rarely. Soon the lower jaw drops from paralysis, allowing the saliva to drivel from the mouth, and the animal can only succeed in closing it momentarily under the greatest provocation to bite. Paralysis of the hind limbs and of the whole body speedily follows, and death ensues in from two to three days. As soon as the jaw is paralyzed the subject is unable to drink, eat, bite, or bark, and emaciation advances with extraordinary rapidity.

The lethargic or tranquil form of rabies in dogs is manifested neither by furious madness nor by palsy of the jaws, but the nervous prostration is shown in a profound lethargy and apathy. The patient curls himself up, and will not be roused by his master's voice, by any noise, disturbance, or even punishment; he makes no response to the caresses of his friends, and pays no attention to the food or drink they bring him, but remains in his place, growing daily more emaciated and lethargic, until relieved by death toward the tenth or fifteenth day of the illness.

Besides the three typical forms there are intermediate varieties, which are classed with one or other according as the symptoms of that type seem to predominate. The same virus, inoculated, will produce different types in separate individuals, the result seeming to depend more on the susceptibility of the subject than any special quality in the poison. With many notable exceptions it may be stated that, on the whole, furious rabies predominates in hounds, bull-dogs, and other less domesticated or naturally vicious and courageous breeds, while the paralytic and tranquil types attack especially house and pet dogs.

POPULAR FALLACIES.—It is a dangerous delusion to suppose that mad dogs have a dread of water and polished surfaces, that they will not eat or drink, that they froth abundantly from the mouth, and that they run with the tail drooping between the hind limbs. There is no hydrophobia in the dog or other domestic animal. The rabid dog drinks freely in the early stages of the disease, lapping even his own urine; later, he still laps, and even plunges his nose in water, though often unable to swallow; and in his wanderings he swims rivers without the slightest reluctance. The appetite is not entirely lost, though greatly impaired and usually depraved, all sorts of unsuitable, noxious, and disgusting objects being picked up and swallowed with avidity. Frothing from the mouth is exceptional in rabies, and the flow of saliva is rarely seen unless when the jaw is paralyzed and pendent. Carrying the tail between the legs is a symptom of all diseases attended by abdominal pain, and is by no means constant in rabies. During the paroxysms the tail is usually carried erect.

Foxes, jackals, and badgers attacked by rabies lose their natural shyness, enter villages, follow and bite other animals and men, and, like rabid dogs, die in an unconscious and paralytic condition. Wolves are affected like foxes, but are more dangerous because of their power, the ferocity of their attack, and their habit of flying at the face and hands. Rabid cats are more retiring than dogs, and show less disposition to attack, but when they do, use both claws and teeth, and especially on bare portions of the body. The cry is hoarse like that emitted during the period of rut. They usually die about the third or fourth day.

The rabid horse is the subject of violent excitement, nervousness, and fear. There are trembling, loss of appetite, rubbing and eversion of the upper lip, neighing, sexual excitement, and inclination to bite and kick. Delirium may be suspected, but during the paroxysms the true nature of the disease is betrayed by the unconquerable desire to bite, kick, and otherwise injure those about him. He will even gnaw the manger and kick the stall to pieces, or lacerate his fore limbs and flanks with his teeth. In the early stages there is the same tendency to lick and rub the wound, which becomes red and irritable, the same red glaring or squinting eyes, and the same jerking of the muscles, as seen in the dog, and the affection winds up in the same way, in paralysis and death in four or five days.

Rabid cattle lose appetite, become very restless and excitable, grind the teeth, lick the cicatrix, evert the upper lip, and otherwise show sexual excitement, bellow often in a loud, terrified manner, as if still apprehensive of the attack of the dog, paw and scrape the ground with the fore feet, butt and kick viciously, have twitching of the muscles, and finally paralysis and death in from four to seven days. When paralysis is coming on the hind feet are often drawn forward as in inflammation of the feet. The pulse and breathing are accelerated during the paroxysms, but I have not found the temperature raised.

Rabid sheep and goats present the same general symptoms, bleat hoarsely, but viciously, have sexual excitement, nibble the cicatrix, have muscular weakness, emaciation, and paralysis, and die in from five to eight days.

Rabid swine show much fear, restlessness, and excitability, hide under the litter, start violently at noises, grunt hoarsely, champ the jaws, show a great disposition to bite and to gnaw and tear objects to pieces, have dark red, glaring eyes, gape and yawn, and become weak and paralytic. Breathing is often labored, and the mucosæ and white skin assume a dull red or leaden hue. Death ensues as early as the fourth or fifth day.

In Herbivora and Omnivora a paroxysm is usually induced by the sight of a dog—a fact of importance in diagnosis.

Rabid skunks have naturally received but little study. They tend, however, to steal up to men and animals and bite some exposed part of the body, like the finger, ear, or nose, and as stealthily retire. It is claimed that their odorous secretion is suppressed.