Chapter II: Preface (2)

We do not ignore the fact that small-pox, like other similar diseases having an epidemic character, may be absent for a length of time from certain districts and then break out again; nor that each epidemic has its period of increment and decrement, and varies in its degree of malignancy. But a full and careful review of the whole history of small-pox since the introduction of vaccination, proves to every unprejudiced mind that every recurring epidemic finds its victims, with comparatively few exceptions, among the unvaccinated, that its spread is arrested by renewed attention to vaccination and its vigorous enforcement, and that, even taking into account the countries and localities where from various causes it has been neglected, the mortality from this foul and fatal disease, small-pox, has been enormously reduced. Human lives have been saved, and human life prolonged to such an extent that it is impossible to estimate the benefits that mankind has derived from the genius and devoted patriotic labours of one man.

That doubts and difficulties in connection with this subject, involving the well-being of the whole human race, have lately arisen, must be admitted. But there is good reason to believe that, by modern researches on the subject of epidemic diseases and the germ theory of disease, these doubts are already being dispelled, and that the difficulties will be speedily obviated.

The grounds for this belief will be understood by the consideration of those scientific investigations to a brief detail of which we now proceed. The reader will then also be better able to judge of the propriety, and necessity of certain measures which, to the uninformed, must appear objectionable or even repulsive and arbitrary.

We now, then, turn to the remarkable experiments and discoveries of M. Pasteur, which have gained for him a world-wide reputation, and the bearing of which on the science of preventive medicine is commanding the attention and admiration of the whole scientific world, and indeed we may say of mankind at large. M. Pasteur is not a medical man, nor, indeed, a physiologist. He is simply a French chemist, a modest, retiring labourer in the field of science whose sole object has been the discovery of truth, and whose chemico-physical researches gained for him the Rumford Medal of the Royal Society in 1856. Having devoted himself specially to the chemistry of organic substances, he was naturally attracted by the discovery of Cagniard de la Tour, that yeast is really a plant, a species of fungus, whose vegetative action in fermentable liquids is the true cause of their fermentation. This was so opposed to the theories of all the chemists of the day, among whom may particularly be mentioned the celebrated Liebig, that it met with their warm opposition. When, however, Helmholtz and others succeeded in showing that by preventing the passage of the minute organisms constituting the yeast plant into fermentable liquids, no fermentation took place, the doctrine soon became established that the first step in the process of alcoholic fermentation is due, not to ordinary chemical changes, but to the presence of living organisms. In like manner the putrefaction and decomposition of various liquids containing organic matter was found to be due, not to the simple action of the oxygen of the atmosphere, but to the introduction from without of microscopic germs which found material for their development in such liquids. So that if by mechanical filtration of the air the entrance of such germs can be prevented, or if by heat or other means they can be destroyed, any fluid, however readily it may undergo putrefaction in ordinary circumstances, will remain perfectly sweet, though freely exposed to the air. And the same fluid will undergo a different kind of fermentation according as it is subjected to the action of different species of germs. These and other facts of scarcely less importance, which cannot here be detailed, induced Pasteur to test the application of the doctrines deduced from them to the study of disease in living animals.

His attention was first directed to the disease affecting the silkworm, and known as the _Pebrine_, which at one time seemed likely to destroy the silk cultivation both in France and Italy. It had been ascertained that the bodies of the silkworm, in all its stages of chrysalis, moth, and worm, were in this disease infested by minute corpuscles which even obtained entrance into the undeveloped eggs. After a prolonged and difficult inquiry, Pasteur found that these minute corpuscles were really independent, self-propagating organisms, introduced from without, and were not merely a sign of the disease, but its real cause. As a result of the application of these discoveries, the silkworm disease has been extinguished, or so controlled as to have saved a most important and valuable culture.

Between the years 1867 and 1870 above 56,000 deaths from a disease variously designated as "anthrax," or "carbuncular disease," and "splenic fever," and in France known by the terms "charbon," or "pustule maligne," are stated to have occurred among horses, cattle, and sheep in one district of Russia, Novgorod, occasioning also the deaths of 528 among the human population. It occurs in two forms, one more malignant and rapid in its action than the other. In France the disease appears to be scarcely ever absent, and is estimated to entail on the breeders of cattle an annual loss of many millions of francs. As a milder epidemic it has prevailed in this country, and the disease which has lately broken out in Bradford and some other towns in the north among wool-sorters, has now been shown to be a modification of the same disease communicated by the wool of sheep that have been infected.

On examining the blood of animals, the subjects of "splenic fever," some French pathologists had discovered the presence of certain minute transparent filaments which, by the investigations of a German physician named Koch, were proved to be a fungoid plant developed from germ particles of microscopic minuteness. By gradual extension these minute particles, termed "microbes," attain the form of small threads or rods, to which the name of "bacilli" has been given, from the Latin _bacillus_, a rod or staff. These rods were found to be in fact hollow tubes, divided at intervals by partitions, which, on attaining full growth, break up into fragments, the interiors of which are found to be full of minute germs similar to those from which the rods were at first developed. These germs were found by Koch and his collaborateurs to be capable of cultivation by being immersed in some suitable organic liquid kept at a proper temperature, and the supply could be kept up by introducing even a few drops of such impregnated fluids into other fluids, and repeating the process again and again. The next step to test the potency of these germs to generate the disease in animals whence they were originally obtained, was to vaccinate animals with a few drops of the fluid thus artificially infected. Accordingly it was found that the bodies of guinea-pigs, rabbits, and mice thus inoculated became infected, and developed all the characteristic symptoms of splenic fever or carbuncular disease.

Pasteur, whose enthusiasm in the pursuit of investigations which had already been crowned with such signal success kept him awake to all that was being done by other inquirers, and made him watchful of every event that transpired relative to the epidemic diseases of cattle, was struck with the fact that some of the most fatal outbreaks of "charbon" among flocks of sheep occurred in the midst of apparently the most healthy pastures. His sagacity led him to inquire what had been done with the carcasses of animals that had died from previous outbreaks of the disease in these localities, when he found that they had been buried in the soil and often at great depths, of the same pastures. But how could the disease germs make their way to the surface from a depth of eight or ten feet? Earthworms, he guessed, might have conveyed them. And notwithstanding the incredulity with which his explanation was received, he forthwith proceeded to verify his supposition. Having collected a number of worms from the ground of the pastures in question, he made an extract of the contents of the alimentary canal of the worms, and with this he inoculated rabbits and guinea-pigs, gave them the "charbon" in its most fatal form, and proved the identity of the malady by demonstrating that the blood of the victims swarmed with the deadly "bacillus." And here we cannot but stop to notice the remarkable confirmation that is thus given to the wonderful and beautiful observations of Darwin as set forth in his last work on "The Formation of Vegetable Mould Through the Action of Worms." Darwin has shown beyond all dispute, as the result of his incomparable researches, that though "the plough is one of the most ancient and most valuable of man's inventions, long before he existed the land was in fact regularly ploughed, and still continues to be ploughed, by earthworms." He has shown us that the smoothness which we admire in a wide, turf-covered expanse "is mainly due to all the inequalities having been slowly leveled by worms," and that "the whole of the superficial mould over any such expanse has passed, and will pass again, every few years, through the bodies of worms!" It was left for Pasteur to show that these innumerable and indefatigable plowmen, whilst rendering to man such efficient service, may also be the carriers of the seeds of disease and death.

In proceeding with our brief historical account of Pasteur's and allied researches, we are arrived at the point where their analogy to Jenner's becomes manifest, and where their direct bearing on the welfare of mankind comes into view. So soon as it was known that these disease germs were low forms of vegetation, and that, like other vegetables, they could be cultivated, it was natural to ask whether, like other vegetables, their characters and properties could not be so modified as to render them at least less deleterious. Every one knows the difference between the crab-apple and its cultivated variety, the sloe and the plum, the wild and the cultivated celery. It is all the difference between unwholesome and wholesome food.

Two methods of cultivation, with a view to obtaining the desired modification of the power exercised by the bacilli and other similar germs, presented themselves, the one analogous to that really pursued by Jenner where small-pox, or the grease of the horse, was passed through the system of the cow, and then from one human being to another; and the second by carrying on the cultivation out of the living body. Both these plans have been adopted, with the result of proving that the potency of the germs can be so diminished as to render the disease produced by their introduction so mild as to be of no importance. Pasteur cultivated the bacillus in chicken broth or meat juice, and allowed a certain time to elapse before he made use of the mixture. After allowing only two months to elapse, the virulence of the germs seemed to be but little impaired, but after three or four months animals inoculated with the fluid, though they took the disease, had it in so mild a form that the greater number recovered. After a long period of six or eight months the engendered disease was so mild that all the animals speedily recovered and regained health and strength.

And now the question will naturally arise, Did animals which had passed through the mild disease thus induced acquire a protection against the original disease, if brought in contact with it in subsequent epidemics, in the same way that Jenner's vaccinated patients were protected against small-pox?

An answer in the affirmative may now be given with the utmost confidence. Experiments conducted, both in this country and abroad, by both methods of procedure, have abundantly proved that animals may be protected by inoculation so as to render them insusceptible of any form of the destructive anthrax disease.

From a remarkable paper read by Pasteur before the International Medical Congress we extract the concluding paragraph. After detailing the method pursued to obtain the requisite attenuation of the virus, and stating that by certain physiological artifices it may be made again to assume its original virulence, he proceeds: "The method I have just explained, of obtaining the vaccine of splenic fever, was no sooner made known then it was very extensively employed to prevent the splenic affection. In France we lose every year by splenic fever animals to the value of 20,000,000 francs, and even, according to one of the persons in the office of the Minister of Agriculture, more than 30,000,000 francs, but exact statistics are still wanting. I was asked to give a public demonstration at Pouilly-le-Fort, near Melun, of the results already mentioned. This experiment I may relate in a few words. Fifty sheep were placed at my disposition, of which twenty-five were vaccinated, and the remaining twenty-five underwent no treatment. A fortnight afterwards the fifty sheep were inoculated with the most virulent anthracoid microbe (or germ). The twenty-five vaccinated sheep resisted the infection, the twenty-five unvaccinated died of splenic fever within fifty hours.

"Since that time the capabilities of my laboratory have been inadequate to meet the demands of farmers for supplies of this vaccine. In the space of fifteen days we have vaccinated in the departments surrounding Paris, more than 20,000 sheep, and a large number of cattle and horses. This experiment was repeated last month at the Ferme de Lambert, near Chartres. It deserves special mention.

"The very virulent inoculation practiced at Pouilly-le-Fort, in order to prove the immunity produced by vaccination, had been effected by the aid of anthracoid germs deposited in a culture which had been preserved in my laboratory more than four years, that is to say, from the 21st March, 1877. There was assuredly no doubt about its virulence, since in fifty hours it killed twenty-five sheep out of twenty-five. Nevertheless, a commission of doctors, surgeons, and veterinary-surgeons, of Chartres, prejudiced with the idea that virus obtained from infectious blood must have a virulence capable of defying the action of what I call cultures of virus, instituted a comparison of the effects upon vaccinated sheep and upon unvaccinated sheep of inoculation with the blood of an animal which had died of splenic fever. The result was identical with that obtained at Pouilly-le-Fort--absolute resistance of the vaccinated and deaths of the unvaccinated. If I were not pressed for time I should bring to your notice other kinds of virus attenuated by similar means. These experiments will be communicated by-and-by to the public."

The bearing of these researches of Pasteur on vaccination with cow-pox, and the whole of the Jennerian doctrines, will be evident. They throw a flood of light both on the efficacy of vaccination and the many supposed failures which have given a handle to the unscrupulous fanatical detractors of Jenner and his doctrines. They go far toward establishing the correctness of the view entertained by Jenner as to the identity of small-pox and cow-pox, showing how great may be the modifications effected in the original virus by repeated transmission, either through the animal or the human system.

But apart from the question of identity or diversity of small-pox and vaccinia, Pasteur's researches prove beyond all question that a disease virus may be both diminished and augmented in power by physiological devices, and that therefore the efficacy of the vaccine lymph may, in various ways, be so diminished as to lose its protective power, without shaking our faith in the principle of vaccination or detracting in the least from the inestimable value of Jenner's discovery. The attention of the scientific world will now be, and is, directed to the important inquiry, How far has the original vaccinia of Jenner lost its protective power? If so, how has this been brought about, and by what means can it be restored? Must we again revert to the cow for a new supply? Need we only be more scrupulous in the selection of the vesicles, and the particular stage of their development, and in the mode in which the operation of vaccination is performed? These and numerous other similar questions are now being discussed and investigated, but none probably is more important than the question how far the protective influence in each individual is dissipated by time, and hence the principle of re-vaccination is now being enforced. There can be no doubt that different epidemics possess different degrees of virulence, and what proves a sufficient protection in a mild epidemic of small-pox may not be sufficient in a more virulent one. In certain seasons and in certain conditions of the atmosphere, the human system is more prone to certain disease than at other times. Pasteur's experiments on cultivated virus or germs show that in the course of time, and in certain conditions of exposure to the action of oxygen or other agents, the vitality, or constitution, so to speak, of the germs may be so changed as materially to alter their action on the animal system. We have, therefore, scientific grounds for reverting from time to time to the heifer for a new stock, rather than continuing to rely on the perpetual transmission from one human body to another.

This is not the place to enter on the whole question of the germ theory of disease, but who does not see how wide is the field for investigation opened up by Pasteur and others? Already the application of the principle of vaccination has been successfully applied by Pasteur to a very fatal epidemic disease attacking fowls, and known by the name of "chicken cholera." By inoculating chickens with the cultivated variety of the particular "bacillus" he has afforded to them complete protection. The economic value of this to France may in some measure be estimated by the many millions of eggs which are exported from France to this country alone. How many other diseases, such as scarlatina and diphtheria, which now carry off annually thousands of children, may not ere long be extinguished by like means who shall say? "I venture," states Mr. Simon, in his address to the Health Section of the International Congress, "to say that in the records of human industry it would be impossible to point to work of more promise to the world than these various contributions to the knowledge of disease and of its cure and prevention, and they are contributions which, from the nature of the case, have come, and could only have come, from the performance of experiments on living animals."

Compulsory vaccination is, no doubt, a strong measure, and one which might, in this land of individual liberty, be expected to give rise both to question and opposition. It can only be justified by proving that it is to the interest of the individual as well as of the whole community that it should be enforced. Of its propriety and necessity we believe it needs only a calm and unprejudiced inquiry to be convinced. Most of the objections raised against it are either baseless or admit of being obviated. That some of the objections are of a character that command our respect may be admitted, but mere sentiment or prejudiced and ill-founded objections, must give place to sound arguments and well-established evidence. In this, as in many similar cases, opposition and discussion open up entrances for light by which the clouds of ignorance and darkness are sure to be dispelled. But even as this whole question of vaccination now stands, the responsibility of those who are persistently misrepresenting facts and misleading the public is great, nay, criminal, when we reflect how many lives are sacrificed by the neglect of precautionary means within the reach of all.

LOUIS PASTEUR AND HIS WORK

PATRICK GEDDES AND J. ARTHUR THOMSON

[Professor Geddes is Professor of Botany at University
College, Dundee. He has written "Chapters in Modern Botany"
and many botanical articles and papers. Professor Thomson is
Regius Professor of Natural History, Aberdeen University. His
works include "The Study of Animal Life," "Outlines of
Zoölogy," "The Natural History of the Year" and "The Science
of Life." "The Evolution of Sex" was written jointly by both
these authors. The article from which extracts follow was
published in the _Contemporary Review_, 1895: the editor's
permission to reprint is gratefully acknowledged. The Life of
Louis Pasteur by M. Radot, 2 vols., were published by
McClure, Phillips & Co., New York, 1901.]

The course of Pasteur's scientific work is one of remarkably natural and logical sequence. As the veteran M. Chevreuil long ago said in the Academy of Sciences, "It is by first examining in their chronological order the researches of M. Pasteur, and then considering them as a whole, that we appreciate the rigor of his conclusions, and the perspicacity of a mind which, strong in the truths which it has already discovered, sweeps forward to the establishment of what is new." We shall therefore summarize the record of his greatest achievements.

As was natural in a pupil of Dumas, Balard, and Delafosse, Pasteur's first important piece of work was chemical and crystallographic, and we may best understand its spirit by recalling the work of Delafosse's master in mineralogy, the Abbé Hauy, who is still remembered for that bold attempt to visualize the ultimate structure of the crystal, to penetrate the inmost secret of its architecture, which also reappears in another way in the work of Mendelejeff. Pasteur's puzzle concerned the tartrates and paratartrates of soda and ammonia. These two salts are alike in chemical composition, in crystalline form, in specific gravity, and so on, but they differ in behaviour. Thus, as Biot had shown, a solution of tartrate deflects the plane of polarized light passed through it, while a solution of the paratartrate does not. The salts are the same, yet they behave differently. A note to the Academy from the famous chemist Mitscherlich emphasized the entire similarity of the two salts, and this acted as an additional stimulus to Pasteur. He succeeded in distinguishing the minute facets which even Mitscherlich had missed; he proved that the paratartrate is a combination of a left-handed and a right-handed tartrate, and did much else which only the expert chemist could duly explain. Biot was first doubtful, then delighted; Arago, who had also busied himself with these matters, moved that Pasteur's paper be printed in the memoirs of the Academy, and Mitscherlich himself congratulated the young discoverer who had tripped him up.

Already, then, in this minute and laborious piece of work, we may detect ultra-microscopic mental vision, and that rigorous accuracy so characteristic of the man. Yet it is interesting to observe that at this early stage he was sowing his wild oats of speculation. Impressed by the strange rotation of the plane of polarization exhibited by these organic salts, he deduced therefrom an hypothesis of molecular dissymmetry, and hazarded the view that this was a fundamental distinction between the organic and the inorganic. For various reasons, neither chemist nor biologist would nowadays accept this distinction; but it is hard to tell what Pasteur might have made of this inquiry had not circumstances, regretted at the time, directed his attention to very different subjects.

Being thus known in connection with tartrates, Pasteur was one day consulted, so the story goes, by a German manufacturer of chemicals, who was puzzled by the fermentation of his commercial tartrate of lime, which contained some admixture of organic impurities. Pasteur undertook to look into the matter, and probably deriving some hint from the previous work of Cagniard Latour, and Schwann who had demonstrated the yeast-plant which causes alcoholic fermentation, he demonstrated the micro-organism which fermented the tartrate of lime. He extended this discovery to other tartrates, and made the neat experiment of showing how the common blue mould (_Penicillium glaucum_), sown in paratartrate of ammonia, uses up all the right-handed tartrate and leaves the left-handed salt alone, its identical chemical composition notwithstanding. These and similar inquiries led him to tackle the whole question of fermentation, but his transference to Lille had probably much to do with this. For, as one of the chief industries of the district is making alcohol from beet-root and grain, Pasteur's practical sense led him to devote some of his lectures to fermentation; here, as always, as his biographer reminds us, wishful to make himself directly useful to his hearers.

The prevalent theory of fermentation, before Pasteur took the subject in hand, was that of Willis and Stahl, revised and elaborated by Liebig. According to this theory, nitrogenous substances in a state of decomposition upset the molecular equilibrium of fermentable matter with which they are in contact. What Pasteur did was to show that lactic, butyric, acetic, and some other fermentations, were due to the vital activity of micro-organisms. In spite of Liebig's prolonged opposition, Pasteur carried his point; and although some of his detailed interpretations have since been revised, it is universally admitted that he changed the whole complexion of the fermentation problem. It must, of course, be borne in mind that his theory of the vital nature of many fermentations does not apply to soluble ferments or enzymes--such as diastase and pepsin--which are chemical substances, not living organisms. Part, indeed, of the opposition to Pasteur's views was due to the fact that this distinction between organized and unorganized ferments was not at the time clearly drawn. Perhaps, indeed, we are as yet by no means out of the woods.

In the course of his work on fermentation, Pasteur made an important theoretical step by distinguishing the micro-organisms which require the presence of free oxygen, from forms which are able to live apart from free oxygen, obtaining what they require by splitting up oxygen-containing compounds in the surrounding medium. These he termed ærobic and anærobic respectively. Practically, this piece of work immediately led to what is known as the Orleans process of making vinegar. Some years later, after he had returned to Paris, he followed this up by his studies on wine, in the course of which he tracked various wine-diseases to their sources, and showed how deterioration might be prevented by raising the wine for a minute to a temperature of 50°C. The wine-tasters of Paris gave their verdict in his favour.

The old notion of spontaneous generation still lingered in some quarters, and in 1858 Pouchet had given new life to the question by claiming before the Academy of Sciences that he had succeeded in proving the origin of microscopic organisms apart from pre-existing germs. But Pasteur knew more than Pouchet as to the insidious ways of germs: he showed the weak point of his antagonist's experiments, and gained the prize, offered in 1860 by the Academy, for "well-contrived experiments to throw new light upon the question of spontaneous generation." As every one knows, the victory was with Pasteur, but the idea is an old and recurrent one, and dies hard. Thus, not many years afterward, Pasteur and Tyndall had to fight the battle over again with Bastian. The important result of what seems at first sight an abstract discussion has been not only an increased knowledge of the distribution and dissemination of bacteria, but the establishment of the fundamental conditions and methods of experimental bacteriology....

[Here follows substantially the same narrative as that given by Sir J. Risdon Bennett on pages 36 to 49 of this volume. It recites how Pasteur devised preventives for the disease which was destroying the silkworms; preventives for splenic fever or anthrax.]

Opposition was an ever-recurrent factor in Pasteur's life. He had to fight for his crystallographic and chemical theories, and for his fermentation theory; he had to fight against the theory of spontaneous generation, and for his practice of inoculating as a preventive against splenic fever; he had to fight for each step. But no part of his work has met with so much opposition and adverse criticism as that concerning hydrophobia, though it is easy to exaggerate the importance of the discussion, in which Pasteur himself took little part. Feeling ran high in this country; hence, when it was announced that Pasteur--surely best qualified to speak--was to write the article Hydrophobia in "Chamber's Encyclopædia," a shower of letters inundated the office; hence the article in question includes an editorially demanded summary of the grounds of the opposition by one of ourselves, and to which therefore we may refer the reader.

While avoiding controversy and partisanship as far as may be, the question remains, What did Pasteur do in regard to hydrophobia? His claims are to have proved, first of all, that the disease was particularly associated with the nervous system. The virus is usually spread through the saliva, but it is not found in the blood or lymph, and it has its special seat in the nerves, brain, and spinal cord. Secondly, he showed that the virus might be attenuated in its virulence. The spinal cord of a rabbit which has died of rabies, is, when fresh, powerfully virulent, but when exposed for a couple of weeks to dry air at a constant temperature of 23°-24°C. it loses its virulence. Thirdly, he showed that inoculation with the attenuated virus rendered an animal immune from infection with rabies. To make the animal immune it has first to be inoculated with infected spinal cord fourteen days old, then with that of thirteen days, and so on till inoculation with almost freshly infected spinal cord is possible. In this way the animal becomes refractory to the infection, and if it be bitten it will not die. Fourthly, he showed that even if the organism had been bitten, it was still possible to save it, unless the wounds were near the head--that is, within close reach of the central nervous system. For in the case of a superficial wound, say on hand or leg, the virus takes some considerable time to spread, and during this period of spreading and incubation it is possible to forestall the virus by inoculation with that which has been attenuated. In this case there is obvious truth in the proverb, "He gives twice who gives quickly." And the outcome was, that while out of a hundred persons bitten, nineteen or twenty will in ordinary circumstances die, "the mortality among cases treated at the Pasteur Institute has fallen to less than 1-2 per cent." According to another set of statistics, a mortality of 40 per cent. has been reduced to 1.3 per cent.; and of 1673 patients treated by Pasteur's method only thirteen died.

As to the adverse criticism of Pasteur's inoculation against rabies, it consists, first and second, of the general argument of the anti-vaccinationists, and thirdly, of specific objections. To the two former the school of Pasteur, of course, replies that the value of human life answers the one, and the results of experience the other; but on these controversies we cannot enter here. The main specific objections we take to be three--that as the micro-organism of rabies has not really been seen, the theory and practice of Pasteur's anti-rabic method lack that stability which is desirable; that the statistics in favor of the Pasteur procedure have been insufficiently criticised; that there have been failures and casualties, sometimes of a tragic nature. In regard to this last point--that deaths have occurred as the result of the supposed cure, instead of from the original infection--we may note that the _possibility_ of such casualties was admitted by the English Investigation Committee (1887), while, on the other hand, Dr. Armand Ruffer, who speaks with much authority, denies with all deliberateness that there is any known case in which death followed as the result of Pasteur's treatment.

Microscopic verification is, of course, most desirable, and statistics are proverbially difficult of criticism. But, on the whole, we think it likely that those who, like ourselves are not medical experts will incline to believe that Sir James Paget, Dr. Lauder Brunton, Professor George Fleming, Sir Joseph Lister, Dr. Richard Quain, Sir Henry Roscoe, and Professor Burdon Sanderson must have had grounds 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 small-pox."

So far a summary of Pasteur's personal life and scientific work, but is it not possible to make a more general and rational estimate of these? So much was his life centred in Paris that most people are probably accustomed to think of him as a townsman; but it is more biologically accurate to recognize him as a rustic, sprung from a strong, thrifty stock of mountain peasants. Nor can his rustic early environment of tanyard and farm, of village and country-side, be overlooked as a factor in developing that practical sense and economic insight which were so conspicuous in his life work. The tanner's son becomes the specialist in fermentation; the country boy is never throughout his life beyond hail of the poultry-yard and the farm-steading, the wine press and the silk nursery; brought up in the rural French atmosphere of careful thrift and minute economies, all centred not round the mechanism or exchange of town industries, but round the actual maintenance of human and organic life, he becomes a great life-saver in his generation.

In short, as we might almost diagrammatically sum it up, the shrewd, minutely careful, yet inquiring rustic, eager to understand and then to improve what he sees, passes in an ever-widening spiral from his rural centre upward, from tan-pit to vat and vintage, from manure-heaps, earthworms, and water-supply to the problems of civic sanitation. The rustic tragedies of the dead cow and the mad dog excite the explanation and suggest the prevention, of these disasters; from the poisoning of rats and mice he passes to suggestive experiments as to the rabbit-pest of Australia, and so in other cases from beast to man, from village to state. And on each radius on which he paused he left either a method or a clew, and set some other inquirer at work. On each radius of work he has left his disciples; for he founded not only an Institute, but a living school, or indeed whole schools of workers. We think of him, then, not only as thinking rustic, but as one of the greatest examples in science of the Rustic Thinker--a type of thinker too rare in our mechanical and urban generation, yet for whom the next generation waits.

As to his actual legacy to the world, let us sum it up briefly. There is the impulse which he gave, after the successful organization of his own Institute, to the establishment in other countries of similar laboratories of preventive medicine, and, one may also say, of experimental evolution. There is his educative work at Strasburg and Lille, at the Ecole Normale and the Sorbonne, and, above all, in the smaller yet world-wide circle of his immediate disciples. To general biology his chief contribution has been the demonstration of the part which bacteria play, not only in pathological and physiological processes, but in the wider drama of evolution. To the chemist he has given a new theory of fermentation; to the physician many a suggestive lesson in the etiology [inquiry into the causes] of diseases, and a series of bold experiments in preventive and curative inoculation, of which Roux's treatment of diphtheria and Professor Fraser's new remedy for snake-bite are examples at present before the public; to the surgeon a stable foundation, as Lister acknowledged, for antiseptic treatment; to the hygienist a multitude of practical suggestions concerning water-supply and drainage, disinfection and burial. On brewer, distiller, and wine-maker he has forced the microscope and its results; and he has shown both agriculturist and stock-breeder how some, at least, of their many more than ten plagues may be either averted or alleviated.

TUBERCULOSIS AND ITS PREVENTION

T. MITCHELL PRUDDEN, M.D.

[Dr. Prudden is Professor of Pathology in the College of Physicians
and Surgeons, New York. He has bestowed especial attention upon
the means of preventing disease: in that important field he has
written three capital manuals, all published by G. P. Putnam's
Sons, New York:--"Story of the Bacteria," "Dust and Its Dangers,"
"Water and Ice Supplies." His other works, intended for the
professional reader, are of the highest authority. The article
here given appeared in _Harper's Magazine_, March, 1894; copyright
by Harper & Brothers, who have granted permission to reprint.
In May, 1902, these pages were revised by Dr. Prudden.]

It is commonly neither wise nor necessary for people not professionally concerned to think much about disease, or weigh anxiously the chance or mode of its acquirement. But now and then conditions arise which demand general attention and instruction regarding certain diseases in order that a great, threatening calamity may be averted. Such a condition faces the people in all lands to-day in the appalling prevalence of tuberculosis. A disease which in mild or severe form affects at least one-half of the whole human race, and which causes the death of full one-seventh of all who pass away, killing about one-third of those who perish between the ages of fifteen and forty-five--a disease which is most insidious in its onset, and often relentless in its course, and which may be largely prevented--is one about which we cannot be indifferent, and should not be longer inactive.

There has long been reason for believing that tuberculosis is a communicable disease. Its prevalence in certain families and communities, its frequent occurrence in those who have personally attended upon its victims, its onset in those who have occupied apartments vacated by consumptives--such facts observed over and over again abundantly justify the belief in its communicability. Up to the commencement of the last decade the cause of the disease was altogether unknown, and no definite data were at hand which could enable us to fix upon a feasible plan for limiting its ravages. But in these later years a great light has been thrown upon this and other kindred diseases.

Most intelligent people are aware that within the past decade a new field in the domain of life has been revealed and widely explored. It has been learned that in earth and air and water there exist countless myriads of living things so minute as to lie far beyond the limits of the unaided vision, and yet in the aggregate so potent in the maintenance of the cycle of life upon earth that without their activity all life would soon cease to be, and the elements which for a short span fall under the sway of the life forces in all higher animals and plants would lapse finally and irrevocably into their primal state. These tiny organisms are called germs, microbes, or micro-organisms. One great and important group of them belongs among the microscopic plants called bacteria. These bacteria as a class are important in their economy of nature, because they live for the most part on dead organic material--that is, such material as has once formed a portion of some living thing.

The world's store of available oxygen, hydrogen, carbon and nitrogen, out of which all living beings are largely formed, is limited, and if after these have served their temporary uses, as the medium through which that mysterious potency called life alone can find expression, they were not speedily released, new generations of living beings could neither assume nor maintain their place in the great cycle of life. And so these tiny plants, year in, year out, by day and by night, unseen and mostly unheeded, are busy always in making possible the return of each year's visible vegetation and the maintenance of an unbroken succession of generations in man and beast.

Different groups and races among the bacteria have different habitations, and vary widely in their special powers. Complex and powerful as is the aggregate result which they accomplish in the world, the performances of the individual are comparatively simple. They are most liberally endowed with the capacity for multiplication, and each germ acts as a tiny chemical laboratory, taking into itself the organic matter on which it feeds, and resolving it into new compounds. Some of the latter are used in building up and maintaining its own body, while others are given off into the surrounding media.

We are but just beginning to peer at the mysterious processes which go on under the influence of the bacteria in this underworld of life, and to realize that all the lore which unwearied toilers in the past have gathered in their studies of the visible forms of animals and plants, makes but one of the many chapters in nature's story-book of life.

But this new and stimulating point of view, toward which the studies of the past decade have led us, does not look so largely into the domain of the practical that it would greatly attract the majority of business and pleasure and _ennui_ ridden mankind were it not for one very practical fact which these recent studies have revealed. This is, that among the myriads of altogether beneficent bacteria which people the earth, and air, and water, there are a few forms which have chosen out of all the world as their most congenial residence the bodies of men. But even this would be of only passing interest to most people were it not still further unfortunately true that in the performance of their simple life-processes these man-loving bacteria, feeding on the tissues of their host, and setting free certain subtle poisons in his blood, each after its kind, can induce those disturbances of the body's functions and those changes in its structure which we call disease.

The diseases caused by the growth of germs in the body are called infectious. The germs causing some of the infectious diseases are given off from the bodies of their victims in such form as to be readily transmitted through the air to others, in whom they may incite similar disease. Such diseases are spoken of as readily communicable, though it is not actually the disease itself, but only the germ causing it, which is transmitted. In other infectious diseases transmission but rarely occurs. Many infectious diseases are very easily communicated from the sick to the well under unsanitary and uncleanly conditions, which with proper care are very little liable to spread.

I need not here put on parade the whole uncanny list of germ diseases, in which tuberculosis stands foremost, followed by pneumonia, diphtheria, typhoid fever, scarlatina, cholera, small-pox, and the rest. Nor need I call to mind the means by which our growing knowledge in this domain has been day by day laid under tribute for suggestions of hope and safety for the stricken. It is a record of brilliant conquest in nature, and already of far-reaching beneficence to man.

But the great fundamental advance which signalizes the past decade is the lifting of this whole class of fateful germ diseases out of the region of the intangible and mysterious, and their establishment, on the basis of positive experimental research, in the domain of the comprehensible and definite. The things which cause them are no longer for us mysterious emanations from the sick, or incorporate expressions of malign forces against which conjurations or prayers could alone promise protection, but they are particulate beings, never self-engendered, never evolved in the body, always entering from without--things which we can see and handle and kill.

Let us now glance at the germ called the tubercle bacillus, the germ which induces and which alone can induce tuberculosis. It does not exist and thrive in the body of men or animals in health. Without the entrance of this particular germ into the human body from without, tuberculosis cannot develop in it. Without the transmission of this germ in some way or other in a living condition from the sick to the well, tuberculosis cannot spread. In the life-story of this tiny germ lie both the potency for mischief which we deplore and the secret of our release from its bondage.

The tubercle bacillus is a little colourless, rod-like plant, so small that even many thousands of them piled together would make a heap far too small to be visible to the naked eye. It cannot move about, nor can it grow without moisture, nor at a temperature much above or much below that of the human body. The material on which it feeds must be very nicely adapted to its requirements, and it has no lurking and growing places in nature outside of the bodies of men and a few warm-blooded animals. It can be cultivated artificially in the laboratory, and we know more about its life and peculiarities than about almost any other germ. While it can remain alive in a dried state for many weeks, it is readily killed by heat, by sunlight, and by many of those chemical substances which we call disinfectants. It does not flourish equally well in the bodies of all human beings.

When once it gains lodgment in a body suited to its growth it multiplies slowly, each germ dividing and subdividing, taking from the tissues material for its growth, and returning to them certain subtle poisons which it sets free. The action of the tubercle bacillus is peculiar in that it stimulates the cells of the body, wherever it may lodge and grow, to the formation of little masses of new tissue, which we call tubercles. These tubercles are as a rule short-lived, and, if the disease progresses, tend to disintegrate. If the tubercles have grown in such situations as to make this possible, as in the intestinal canal or the lungs, the disintegrated and broken-down material, often containing myriads of the living germs, may be cast off from the body. In tuberculosis of the lungs, or consumption, this waste material is thrown off with the sputum [spittle]. While almost any part of the body may be affected, tuberculosis of the lungs is by far the most common form of the disease.

It follows from what has been said that the only way in which we can acquire tuberculosis is by getting into our bodies tubercle bacilli from tuberculous men or animals. The only animals liable to convey the disease to man are tuberculous cattle, and these through the use of either meat or milk. The danger from the use of uncooked meat or the unboiled milk from tuberculous cattle is real and serious, but it will not be considered here at length, because the great and prevailing danger of infection comes from another source.

Almost as soon as the significance of the tubercle bacillus was established, a series of studies was undertaken on the possibility of the spread of the disease by the breath or exhalations of the persons of consumptives. These studies at once showed that the tubercle bacillus cannot be given off into the air of the breath from the moist surfaces of the mouth and air passages, nor from any material which may come from them while this material remains moist, nor from healthy unsoiled surfaces of the body. The establishment of this fact is of far-reaching consequence, because it shows that neither the person nor the breath of the consumptive is a direct source of danger, even to the most constant and intimate attendants.

While the discharges from the bowels in persons suffering from tuberculosis of the intestinal tract may contain many living bacilli, the usual mode of disposal of these discharges protects us from any considerable danger from this source.

It is the sputum after its discharge from the body on which our attention must be fixed. While the sputum is moist it can, as a rule, do no harm, unless it should be directly transmitted to those who are well by violent coughing, sneezing, etc., by the use of uncleansed cooking or eating utensils, by soiled hands, or by such intimate personal contact as kissing or fondling. But if in any way the sputum becomes dried, on floors or walls or bedding, on handkerchiefs or towels, or on the person of the patient, it may soon become disseminated in the air as dust, and can thus be breathed into the lungs of exposed persons.

The wide distribution of tubercle bacilli in the air of living-rooms, and in other dusty places where people go, is due partly to the frequency of the disease and the large numbers of living bacilli which are cast off in the sputum (sometimes millions in a day), and partly to the fact that many of the victims of consumption go about among their fellows for purposes of business or pleasure for months or years. So each consumptive, if not intelligently careful, may year after year be to his fellow-men a source of active and serious and continual infection.

This, then, the dried, uncared-for sputum of those suffering from pulmonary tuberculosis, is the great source of danger; this the means so long concealed by which a large part of the human race prematurely perishes. Let but this discharged material be rendered harmless or destroyed before it dries in all cases, and the ravages of this scourge would largely cease. This is not a theoretic matter only, for again and again have the living and virulent germs been found clinging to the walls and furniture and bedding and handkerchiefs of consumptive persons, and in the dust of the rooms in which they dwell. A malady whose victims far outnumber those of all other infectious diseases put together, sparing neither rich nor poor, seizing upon life while it is as yet only a promise, but most inexorable in the fulness of its tide--this malady can be largely prevented by the universal and persistent practice of intelligent cleanliness.

We have learned in the past few years one fact about tuberculosis which is of incalculable comfort to many, and that is that the disease is not hereditary. It is very important that we should understand this, because it seems to contradict a long-prevalent tradition, and a belief still widely and sorrowfully entertained. Bacteria, and especially most disease-producing bacteria, are very sensitive in the matter of growth and reproduction to the conditions under which they are placed, and especially to the material on which they feed. So that a germ which can induce serious disease in one species of animal is harmless in the body of a different though closely allied form. More than this, different individuals of the same species, or the same individual at different times, may have the most marked differences in susceptibility in the presence of disease-producing germs. What this subtle difference is we do not know. Whether the body at one time affords a congenial soil to the invading germs and at another does not, whether its marvelous and complex powers of resisting the virulent tendencies of disease-producing bacteria at one period or in one individual are more vigorous than in another, and vary at different times, we do not certainly know. This, however, we do know, that certain individuals are more likely than others to yield to the incursions of the tubercle bacillus. This vulnerability in the presence of invading germs we call susceptibility, and susceptibility to the action of the tubercle bacillus is hereditary. It is not the disease, tuberculosis, which comes into the world with certain individuals or with successive children of the same family, but the aptitude to contract it should external conditions favour. What subtle impress on the cells which are to develop into the new individual renders him more than another an easy prey to the tubercle bacillus should it later find lodgment in his body we do not know, and we may not hope soon to be enlightened, since all the intricate mysteries of heredity seem involved in the problem. But this we do know, that how ever much the child of tuberculous parents or a member of a tuberculous family may be predisposed to the disease, he cannot acquire tuberculosis unless by some mischance the fateful germ enters his body from without. What has been all through these years regarded as the strongest proof of the hereditary transmission of tuberculosis--namely, the occurrence of the disease in several members of the same household--is, in the new light, simply the result of household infection--the breathing of air especially liable to contain the noxious germs, or their entrance in some other way into the bodies of persons especially sensitive to their presence. I do not mean to imply that under no conditions can the tubercle bacillus be transmitted from the mother to the child before its birth. In a few instances this is believed to have happened. But its occurrence is so extremely infrequent that it may be regarded as accidental, and of no serious importance from our present point of view.