ence of a poison vaccine cultivable at will； and which can be increased indefinitely in the space of a few hours without having recourse to infected blood。〃＇8＇
This announcement was immediately challenged in a way that brought it to the attention of the entire world。 The president of an agricultural society； realizing the enormous importance of the subject； proposed to Pasteur that his alleged discovery should be submitted to a decisive public test。 He proposed to furnish a drove of fifty sheep half of which were to be inoculated with the attenuated virus of Pasteur。 Subsequently all the sheep were to be inoculated with virulent virus； all being kept together in one pen under precisely the same conditions。 The 〃protected〃 sheep were to remain healthy； the unprotected ones to die of anthrax； so read the terms of the proposition。 Pasteur accepted the challenge； he even permitted a change in the programme by which two goats were substituted for two of the sheep； and ten cattle added； stipulating； however； that since his experiments had not yet been extended to cattle these should not be regarded as falling rigidly within the terms of the test。
It was a test to try the soul of any man； for all the world looked on askance； prepared to deride the maker of so preposterous a claim as soon as his claim should be proved baseless。 Not even the fame of Pasteur could make the public at large； lay or scientific； believe in the possibility of what he proposed to accomplish。 There was time for all the world to be informed of the procedure； for the first 〃preventive〃 inoculationor vaccination； as Pasteur termed itwas made on May 5th； the second on May 17th； and another interval of two weeks must elapse before the final inoculations with the unattenuated virus。 Twenty…four sheep； one goat； and five cattle were submitted to the preliminary vaccinations。 Then； on May 31 st； all sixty of the animals were inoculated； a protected and unprotected one alternately； with an extremely virulent culture of anthrax microbes that had been in Pasteur's laboratory since 1877。 This accomplished； the animals were left together in one enclosure to await the issue。
Two days later； June 2d； at the appointed hour of rendezvous； a vast crowd； composed of veterinary surgeons； newspaper correspondents； and farmers from far and near； gathered to witness the closing scenes of this scientific tourney。 What they saw was one of the most dramatic scenes in the history of peaceful sciencea scene which； as Pasteur declared afterwards； 〃amazed the assembly。〃 Scattered about the enclosure； dead； dying； or manifestly sick unto death； lay the unprotected animals； one and all； while each and every 〃protected〃 animal stalked unconcernedly about with every appearance of perfect health。 Twenty of the sheep and the one goat were already dead； two other sheep expired under the eyes of the spectators； the remaining victims lingered but a few hours longer。 Thus in a manner theatrical enough； not to say tragic； was proclaimed the unequivocal victory of science。 Naturally enough； the unbelievers struck their colors and surrendered without terms； the principle of protective vaccination； with a virus experimentally prepared in the laboratory； was established beyond the reach of controversy。
That memorable scientific battle marked the beginning of a new era in medicine。 It was a foregone conclusion that the principle thus established would be still further generalized； that it would be applied to human maladies； that in all probability it would grapple successfully； sooner or later； with many infectious diseases。 That expectation has advanced rapidly towards realization。 Pasteur himself made the application to the human subject in the disease hydrophobia in 1885； since which time that hitherto most fatal of maladies has largely lost its terrors。 Thousands of persons bitten by mad dogs have been snatched from the fatal consequences of that mishap by this method at the Pasteur Institute in Paris； and at the similar institutes； built on the model of this parent one； that have been established all over the world in regions as widely separated as New York and Nha…Trang。
SERUM…THERAPY
In the production of the rabies vaccine Pasteur and his associates developed a method of attenuation of a virus quite different from that which had been employed in the case of the vaccines of chicken cholera and of anthrax。 The rabies virus was inoculated into the system of guinea…pigs or rabbits and； in effect； cultivated in the systems of these animals。 The spinal cord of these infected animals was found to be rich in the virus； which rapidly became attenuated when the cord was dried in the air。 The preventive virus； of varying strengths； was made by maceration of these cords at varying stages of desiccation。 This cultivation of a virus within the animal organism suggested； no doubt； by the familiar Jennerian method of securing small…pox vaccine； was at the same time a step in the direction of a new therapeutic procedure which was destined presently to become of all…absorbing importancethe method； namely； of so…called serum…therapy； or the treatment of a disease with the blood serum of an animal that has been subjected to protective inoculation against that disease。
The possibility of such a method was suggested by the familiar observation； made by Pasteur and numerous other workers； that animals of different species differ widely in their susceptibility to various maladies； and that the virus of a given disease may become more and more virulent when passed through the systems of successive individuals of one species； and； contrariwise； less and less virulent when passed through the systems of successive individuals of another species。 These facts suggested the theory that the blood of resistant animals might contain something directly antagonistic to the virus； and the hope that this something might be transferred with curative effect to the blood of an infected susceptible animal。 Numerous experimenters all over the world made investigations along the line of this alluring possibility； the leaders perhaps being Drs。 Behring and Kitasato； closely followed by Dr。 Roux and his associates of the Pasteur Institute of Paris。 Definite results were announced by Behring in 1892 regarding two important diseasestetanus and diphtheriabut the method did not come into general notice until 1894； when Dr。 Roux read an epoch…making paper on the subject at the Congress of Hygiene at Buda…Pesth。
In this paper Dr。 Roux； after adverting to the labors of Behring； Ehrlich； Boer； Kossel； and Wasserman； described in detail the methods that had been developed at the Pasteur Institute for the development of the curative serum； to which Behring had given the since…familiar name antitoxine。 The method consists； first； of the cultivation； for some months； of the diphtheria bacillus （called the Klebs…Loeffler bacillus； in honor of its discoverers） in an artificial bouillon； for the development of a powerful toxine capable of giving the disease in a virulent form。
This toxine； after certain details of mechanical treatment； is injected in small but increasing doses into the system of an animal； care being taken to graduate the amount so that the animal does not succumb to the disease。 After a certain course of this treatment it is found that a portion of blood serum of the animal so treated will act in a curative way if injected into the blood of another animal； or a human patient； suffering with diphtheria。 In other words； according to theory； an antitoxine has been developed in the system of the animal subjected to the progressive inoculations of the diphtheria toxine。 In Dr。 Roux's experience the animal best suited for the purpose is the horse； though almost any of the domesticated animals will serve the purpose。
But Dr。 Roux's paper did not stop with the description of laboratory methods。 It told also of the practical application of the serum to the treatment of numerous cases of diphtheria in the hospitals of Parisapplications that had met with a gratifying measure of success。 He made it clear that a means had been found of coping successfully with what had been one of the most virulent and intractable of the diseases of childhood。 Hence it was not strange that his paper made a sensation in all circles； medical and lay alike。
Physicians from all over the world flocked to Paris to learn the details of the open secret； and within a few months the new serum…therapy had an acknowledged standing with the medical profession everywhere。 What it had accomplished was regarded as but an earnest of what the new method might accomplish presently when applied to the other infectious diseases。
Efforts at such applications were immediately begun in numberless directionshad； indeed； been under way in many a laboratory for some years before。 It is too early yet to speak of the results in detail。 But enough has been done to show that this method also is susceptible of the widest generalization。 It is not easy at the present stage to sift that which is tentative from that which will be permanent； but so great an authority as Behring does not hesitate to affirm that today we possess； in addition to the diphtheria antitoxine； equally specific antitoxines of tetanus； cholera； typhus fever； pneumonia； and tuberculosisa set of diseases which in the aggregate account for a startling proportion of the general death…rate。 Then it is known that Dr。 Yersin； with the collaboration of his former colleagues of the Pasteur Institute； has developed； and has used with success； an antitoxine from the microbe of the plague which recently ravaged China。
Dr。 Calmette； another graduate of the Pasteur Institute； has extended the range of the serum…therapy to include the prevention and treatment of poisoning by venoms； and has developed an antitoxine that has already given immunity from the lethal effects of snake bites to thousands of persons in India and Australia。
Just how much of present promise is tentative； just what are the limits of the methodsthese are questions for the future to decide。 But； in any event； there seems little question that the serum treatment will stand as the culminating achievement in therapeutics of our century。 I