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Rh of doctrines, Cohnheim reaffirmed the infectivity of the disease, and even made the proof of tubercle depend on inoculation alone: “everything is tuberculous that can produce tuberculous disease by inoculation in animals that are susceptible to the disease; and nothing is tuberculous that cannot do this.” In 1881 Koch discovered the tubercle bacillus, and, in spite of the tragic failure of his tuberculin in 1890-91, a vast amount of practical advantage has already issued out of Koch's discovery, both by way of cure and by way of prevention. It has been proved, by experiment on animals, that the sputa of phthisical patients are infective; and this and the like facts have profoundly influenced the nursing and general care of such cases. Bacteriology has brought about (under the safeguard of modern methods of surgery) a thorough and early surgical treatment of all primary tuberculous sores or deposits—the excision of tuberculous ulcers, the removal of tuberculous glands and the like. It has helped us to make an early diagnosis, in obscure cases, by finding tubercle bacilli in the sputa, or in the discharges, or in a particle of the tissues. It has proved, past all reasonable doubt, that tabes mesenterica, a disease that kills every year in England alone many thousands of children, may arise from infection of the bowels by the milk of tuberculous cows. And it has helped to bring about the present rigorous control of the milk trade and the meat trade.

The “new tuberculin,” now that the use of the opsonic index has guided physicians to a better understanding of the tuberculin treatment, has been found of great value, and is giving excellent results in suitable cases. Moreover, tuberculin is used, because of the reaction that it causes in tuberculous animals, as a test for the detection of latent tuberculosis in cattle. An injection of one to two cubic centimetres under the skin of the neck is followed by a high temperature if the animal be tuberculous. If it be not, there is no rise of temperature, or only a very slight rise. For example, in 1899 this test was applied to 270 cows on farms in Lancashire: 180 reacted to the test, 85 did not, 5 were “doubtful.” Tuberculous disease was actually found in 175 out of the 180. Eber of Dresden used the test on 174 animals, of whom 136 reacted, 32 did not react and 6 were doubtful. Of the 136, 22 were slaughtered, and were all found to have tubercle; of the 32, 3 were slaughtered, and were found free. The opinion of Professor M'Fadyean, one of the highest authorities on the subject, is as follows: “I have most implicit faith in tuberculin as a test for tuberculosis when it is used on animals standing in their own premises and undisturbed. It is not reliable when used on animals in a market or slaughter-house. A considerable number of errors at first were found when I examined animals in slaughter-houses after they had been conveyed there by rail, &c. Since that, using it on animals in their own premises, I have found that it is practically infallible. I have notes of one particular case where 25 animals in one dairy were tested, and afterwards all were killed. There was only one animal which did not react, and it was the only animal not found to be tuberculous when killed.” This test has now been in regular use for many years in many countries, and it is accepted everywhere as of national importance.

5. Diphtheria.—The Bacillus diphtheriae (Klebs-Löffler bacillus) was described by Klebs in 1875, and obtained in pure culture by Löffler in 1884. Behring and Kitasato, in 1890, succeeded in immunizing animals against the disease. The first cases treated with diphtheria antitoxin were published in 1893 by Behring, Kossel and Hübner. In England the antitoxin treatment was begun in the latter part of 1894. Besides its curative use, the antitoxin has also been used as a preventive, to stop an outbreak of diphtheria in a school or institute or hospital or village, and with admirable success. (See .)

6. Tetanus (lock-jaw).—Experiments on animals have taught us the true nature of this disease, and have led to the discovery of an antitoxin which has given fairly good results. We possess, moreover, a preventive treatment against the disease; though, unfortunately, the time of latency, when the antitoxin is most needed, cannot be recognized. The old, mischievous doctrine that tetanus was due to acute inflammation of a nerve, tracking up from a wound to the central nervous system, was abolished once and for ever by Sternberg (1880), Carle and Rattone (1884) and Nicolaier (1884), who proved that the disease is due to infection by a specific flagellate organism in superficial soil. “It is said to be present in almost all rich garden soils, and that the presence of horse-dung favours its occurrence. There seems to be no doubt as to the ubiquity of the tetanus germ” (Poore, Milroy Lectures, 1899). The work of discovering and isolating the bacillus was full of difficulty. Nicolaier, starting from the familiar fact that the disease mostly comes from wounds or scratches contaminated with earth, studied the various microbes of the soil, and inoculated rabbits with garden mould. He produced the disease, and succeeded in finding and cultivating the bacillus, but failed to obtain a pure culture. Kitasato, in 1899, obtained a pure culture. Others studied the chemical products of the bacillus, and were able to produce the symptoms of the disease by injection of these chemical products obtained from cultures, or from the tissues in cases of tetanus. It has been proved that the infection tends to remain local; that the bacilli in and near the wound pour thence into the

blood their chemical products, and that these have a selective action, like strychnine, on the cells of the central nervous system. Therefore the rule that the wounded tissues should be at once excised, in all cases where this can possibly be done, has received confirmation. Before Nicolaier, while men were still free to believe that tetanus was the result of an acute ascending neuritis, this rule was neither enforced nor explained.

As a preventive against tetanus, in man or in animals, the antitoxin has proved of the very utmost value. This has been shown in a striking way in America. “One of the wounds most commonly followed by lock-jaw is the blank-cartridge wound of the hand common on the glorious Fourth of July. The death-rate from these wounds is appalling. An active campaign has been conducted throughout the medical profession to reduce this mortality. All over the country, surgeons and medical journals have advised the injection of tetanus antitoxin in every case of blank-cartridge wound. The American Medical Association has compiled statistics of Fourth of July fatalities for the past six years. In 1903, the Fourth of July tetanus cases numbered 416. Then physicians began a more general use of antitoxin in all cases of blank-cartridge and common cracker wounds. As a result of this campaign of prophylaxis by antitoxin injections, from 416 cases of tetanus in 1903 the number dropped to 105 cases in 1904, 104 cases in 1905, 89 cases in 1906, 73 cases in 1907 and 55 cases in 1908. This reduction in the number of tetanus cases took place while the number of accidents remained practically the same each year, and while the number of deaths from causes other than tetanus was steadily rising from 60 in 1903 to 108 in 1908. It is thus evident that the saving of at least 300 lives from tetanus has been accomplished each year through the prophylactic use of antitoxin in the cases of Fourth of July wounds alone” (James P. Warbasse, M.D ., The Conquest of Disease through Animal Experimentation, Appleton & Co., 1910).

The preventive use of the serum in veterinary practice has yielded admirable results. In some parts of the world tetanus is terribly common among horses. Nocard of Lille has reported as follows: “The use of anti-tetanus serum as a preventive has been in force for some years in veterinary practice in cases of wounds or surgical procedures. To this end the Pasteur Institute has supplied 7000 doses of anti-tetanus serum, a dose being 10 cubic centimetres; a quantity which has sufficed to treat preventively 3100 horses in those parts of the country where tetanus is endemic. Among these there has been no death from tetanus. In the case of one horse, injected five days after receiving a wound, tetanus developed, but the attack was slight. During the same time that these animals were injected, the same veterinary surgeon observed, among animals not treated by injection, 259 cases of tetanus” (Lancet, August 7, 1897).

7. Rabies (hydrophobia).—The date of the first case treated by Pasteur's preventive method—Joseph Meister, an Alsatian shepherd-boy—is July 1885. The existence of a specific micro-organism of rabies was a matter of inference. The incubation period of the disease is so variable that no preventive treatment was possible unless this incubation period could be regulated. Inoculations of the saliva of a rabid animal, introduced under the skin of animals, sometimes failed; and if they succeeded, the incubation period of the disease thus induced was hopelessly variable. Next, Pasteur used not saliva, but an emulsion of the brain or the spinal cord; because the central nervous system is the chief seat of the poison. But this emulsion, introduced under the skin, was also uncertain in action, and gave no fixed incubation period. Therefore, he argued, as the poison has a selective action on the nerve cells of the central nervous system, and a sort of natural affinity with them, it must be introduced directly into them, where it will have its proper environment; the emulsion must be put not under the skin, but under the dura mater (the membrane enveloping the brain). These subdural inoculations were the turning-point of his work. By transmitting the poison through a series of rabbits, by subdural inoculation of each rabbit with a minute quantity of nerve tissue from the rabbit that had died before it, he was able to intensify the poison, to shorten its period of incubation, and to fix this period at six days. Thus he obtained a poison of exact strength, a definite standard of virulence, virus fixe: the next rabbit inoculated would have the disease in six days, neither more nor less. By gradual drying, after death, of the cords of rabid animals, he was able to attenuate the poison contained in them. The spinal cord of a rabbit that has died of rabies slowly loses virulence by simple drying. A cord dried for four days is less virulent than a cord dried for three, and more virulent than a cord dried for five. A cord dried for a fortnight has lost all virulence; even a large dose of it will not produce the disease. By this method of drying, Pasteur was able to keep going one or more series of cords, of known and exactly graduated strengths, according to the length of time they had been dried, ranging from absolute non-virulence through every shade of virulence.

As with fowl cholera and anthrax, so with rabies: the poison, attenuated till it is innocuous, can yet confer immunity against a stronger dose of the same poison. A man, bitten by a rabid animal, has at least some weeks of respite before the disease can break out; and during that time of respite he can be immunized against the disease, while it is still dormant. He begins with a dose of poison attenuated past all power of doing harm, and advances day by day