From plague hospitals the returns show that among those of the attacked who were previously inoculated the mortality is reduced to less than one half of that among patients who were not inoculated. The property of reducing the case mortality thus appears to belong to the plague prophylactic in an unmistakable degree.
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By the anti-cholera and anti-plague inoculation the methods of preventive treatment by means of cultivated bacteria and their products have been rendered, so to say, a part of the daily policy in human medicine. The usefulness and practicability of those methods have become clearly apparent, and steps have been taken to extend further the field of their application. On the ground of the experiments made with the typhoid bacillus in the Pasteur Institute in 1889–’93, and of the results obtained from the anti-cholera inoculation in India, I was able to induce Professor Wright, of the Pathological Laboratory in Netley, whom I initiated in 1892 in the principles and technique of anti-cholera inoculation, to start a campaign of similar operations against typhoid among the British troops. The latter are stationed at different times of their service very nearly in all parts of the world, and yearly pay a very heavy tribute to that disease. The medical officers in charge of these troops pass through a course of training at Netley, and Professor Wright had rendered excellent services in connection with the cholera inoculations, by disseminating the knowledge of them among the probationers of the school. It seemed to me expedient, therefore, to start the typhoid inoculation also through the staff and pupils of that school. The following plan as to the preparation of the vaccine, and the way of carrying out the inoculation, was laid before Professor Wright. The typhoid bacillus was to be brought to a fixed stage of virulence by the inoculation in the peritoneal cavity of Guinea pigs, according to the exact rules prescribed for the anti-cholera inoculation. Once the virus was fixed, it was to be cultivated for twenty-four hours on a solid medium, and a first vaccine prepared by carbolizing that virus. As, however, the durability of the effect of carbolized vaccine alone was not known, this was to be followed up by the injection of a dose of the fixed living virus.
The inoculation was first to be made on volunteers among the physicians on probation at Netley; then on volunteers among the young officers of the army on the eve of their departure for the tropics; and then, with the approval of the military authorities, on volunteers among private soldiers. At the end of 1895, during my visit to England, I obtained from Sir William Mackinnon, then Director-General of the Army Medical Department, permission for Professor Wright to start the work upon the plan above detailed; and the first inoculations, in the way described above, were done in the middle of 1896. Soon after that, Pfeiffer and Kolle, recognizing the same similarity between the cholera and typhoid microbes, and pointing out that the results obtained by us in India were likely to be repeated when applying the method to typhoid, proposed and started a similar series of inoculations.
When the inoculation against plague was begun, and observation showed that dead vaccines alone were apparently sufficient to produce satisfactory results, a second inoculation with living virus appeared less urgently necessary; and as the effect of such an inoculation, which Professor Wright very courageously tried first on himself, seemed troublesome, it was decided to do for the time being the second inoculation also with the carbolized virus. Similarly, the plan which was adopted for the plague inoculation, of cultivating the vaccine in a liquid, instead of a solid medium, and of using cultures of several weeks’ duration, has been subsequently adopted in the typhoid inoculation also.
Many thousands of British soldiers and civilians have already undergone the inoculation in question. The latter was done partly with vaccines cultivated on a solid medium, according to the older plan, and partly with vaccines prepared according to the plague inoculation method. The results so far observed are encouraging, and, I hope, will shortly be improved considerably. At the last Harveian dinner in London, Surgeon-General Jameson, Director-General of the Army Medical Department, summarized the results of the observations in India, where, among several thousands of young soldiers, the most prone to the disease, the incidence of typhoid since their inoculation was 0.7 per mille, while among the older, more resistant, not inoculated soldiers, the incidence was during the same period just double that. A large proportion of the force now on service in the South African campaign have been inoculated, some before embarking and others on their way out.
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Such is the position of preventive inoculation, as applied, so far, to human communities. The very success of these operations is now apt to create some sort of feigned or earnest alarm, and one meets at present with the question, What is going to happen to our poor body if we are to be inoculated against all diseases? and with this other one, How do you expect us to make a living if you try to keep all of us alive? The humorous form of these questions usually permits of their dropping out of the conversation without a reply. The earnest answers are, however, obvious. The efforts of the bacteriologists in combating diseases are at present directed to a twofold aim: their prevention, by a prophylactic treatment, and their cure. The advantage of a curative treatment is that it is to be applied to a relatively small number of persons, to those who actually fall victims to an attack; while that of the preventive treatment is in the greater certainty with which safety and protection are secured by it. The relative position of the two treatments will, in practice, differ in different diseases—namely, according to the prevalence and fatality of a given disease, and according to the merits of the two treatments as they stand at the time. In diseases in which the risks of being attacked are smaller, or the consequences of an attack less serious, or for which a very effective and sure curative treatment has been discovered, the majority of people will prefer to wait for an actual attack rather than to undergo the discomfort of a preventive treatment; in diseases, on the contrary, in which the chances of being attacked are great, or in which the fatality is higher, the sequelæ of an attack more serious, and for which a successful and not very troublesome preventive treatment has been found, large numbers will undergo preventive inoculation. But, even in the latter case, a mutual co-operation between the two methods will exist always, as there will always be a number of people, either among those who have neglected to protect themselves by inoculation, or among those in whom the inoculation has proved unsuccessful, who will fall victims to an attack and require the benefits of a curative treatment, be those at the time little or great.
The answer to the second question is of course to be expected rather from the politico-economist, the wise administrator, the civilian, than from the bacteriologist. In any case it is clear already that if we are ever to be told that we must thin our ranks, we shall prefer not to leave the task in the hands of the indiscriminating microbe, but to have some voice in the matter ourselves. Inoculation marks only the conquest of another force which henceforth we shall be glad to control.
Bombay, India, March, 1900.