scientific physician of his time),—as the expression of the effect produced in the blood by the introduction of a specific poison (such as that of small-pox, measles, scarlatina, cholera, typhus, &c.), had naturally directed the attention of thoughtful men to the question (often previously raised speculatively), whether these specific poisons are not really organic germs, each kind of which, a real contagium vivum, when sown in the circulating fluid, produces a definite zymosis of its own, in the course of which the poison is reproduced with large increase, exactly after the manner of yeast in a fermenting wort. Pasteur's success brought this question to the front, as one not to talk about, but to work at; the lead being taken, I believe, by M. Chauveau, the distinguished Professor of Medicine at Lyons; but other investigators (among them our own Prof. Burdon Sanderson) following closely in his wake.-Pasteur's own attention seems at that time to have been chiefly directed to what may be termed the pathology of beer, wine, and vinegar, and to the fight he had still to maintain with the advocates of abiogenesis. I shall not stop to describe the valuable improvements he has introduced into the manufacture of alcoholic and acetous liquors, with a view of preventing those injurious fermentations which often interfere with the normal processes, and sometimes ruin their results ; but shall keep to the object I have specially in view, the exposition of those more recent contributions to preventive medicine,' wbich constitute him the greatest public benefactor of his time.

An epizootic malady extensively prevails on the Continent of Europe, though fortunately but little known in this country, which is sometimes designated splenic fever, and sometimes

or carbuncular' disease, while it is known in France as charbon' or 'pustule maligne. In its most malignant form, it causes the death of the horses, cattle, and sheep affected by it, in the course of four-and-twenty hours. In the less severe form of anthrax disease it occasions great and prolonged suffering, even when final recovery takes place. Both forms seem propagable to man. Between the years 1867 and 1870, above 56,000 deaths from this disease are recorded as having occurred among horses, cattle, and sheep, and 528 deaths among the human population, in the single district of Novgorod in Russia. It appears to be scarcely ever absent from France, and is estimated to involve an annual loss of many millions of francs on the part of breeders in that country; whole flocks and herds being carried off at once, and their proprietors ruined. A mild epizootic of this type seems to have prevailed in this country between 1850 and 1860; while the plague of boils,' under which many of our human population (my unhappy self among the rest) suffered during some part of that decennium, was probably brought on us by infection from animals. Attention has lately been drawn to a severe and often fatal malady occurring among the wool-sorters' at Bradford,

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which is pretty certainly a modification of splenic fever,' communicated by the wool of sheep infected with that disease.

As far back as 1850 it was observed by two distinguished French pathologists, MM. Rayer and Davaine, that the blood of animals affected with splenic fever contained minute transparent rods; but their fungoid nature and life-history was first worked-out a few years since by a young German physician named Koch, whose account of it was soon confirmed by Cohn, the eminent Botanical Professor of Breslau, and afterwards in this country by Mr. Ewart, all of whom cultivated' the plant in aqueous humour, or some other organic liquid of suitable character, kept at nearly blood-heat. They found the “rods' to be produced by progressive extension from germ-particles of extreme minuteness. At first they are simple tubes divided at intervals by transverse partitions ; but after a time minute dots are seen within these tubes, which gradually enlarge into ovoid bodies that lie in rows within the rods; and at last the rods fall to pieces, liberating the germ-particles they included. The minutest drop of the fluid containing these germs, if conveyed into another portion of cultivated (uid, initiates the same process of growth and reproduction; and this may be repeated many times without any impairment of the potency of the germs, which, when introduced by inoculation into the bodies of rabbits, guinea-pigs, and mice, develope in them all the characteristic phenomena of splenic fever. Koch further ascertained that the blood of animals that succumbed to this disease might be dried and kept for four years, and might be even pulverised into dust, without losing its power of infection.

Here I would stop to cite the prophetic words used by Professor Tyndall, when giving an account to a Glasgow audience, in 1876, of Koch's then recent researches :-The very first step towards the extirpation of these contagia is the knowledge of their nature; and the knowledge brought to us by Dr. Koch will render as certain the stamping out of splenic fever, as the stoppage of the plague of pébrine by the researches of Pasteur.'

It was but fitting that the complete verification of this prediction should be the direct result of the labours of the illustrious man on whose previous work it was based; although others were at work, more or less successfully, in the same direction.

One of the first questions examined by Pasteur was the cause of outbreaks of charbon ’ in its most deadly form among flocks of sheep feeding in what appeared to be the healthiest pastures, far removed from any obvious source of infection. Learning by the inquiries he instituted that special localities seemed haunted, at distant intervals, by this plague, he inquired what had been done with the bodies of the animals that had died of it; and learned that it had been customary to bury them deep in the soil, and that such interments had been made, it might have been ten years before, beneath the surface of some of the very pastures in which the fresh outbreaks took place. Notwithstanding that the depth (ten or twelve feet) at which the carcases had been buried, seemed to preclude the idea of the upward travelling of the poison-germs, the divining mind of Pasteur found in earth-worms a probable means of their conveyance; and he soon obtained an experimental verification of his idea, which satisfied even those who were at first disposed to ridicule it. Collecting a number of worms from these pastures, he made an extract of the contents of their alimentary canals; and found that the inoculation of rabbits and guinea-pigs with this extract gave them the severest form of charbon,' due to the multiplication in their circulating current of the deadiy anthrax-bacillus, with which their blood was found after death to be loaded.

Another mode in which the disease-germs of anthrax may be conveyed to herds of cattle widely separated from each other and from any ostensible source of infection, was discovered by the inquiries prosecuted, a few years ago, by Professor Burdon Sanderson at the Brown Institution, in consequence of a number of simultaneous outbreaks which occurred in different parts of the country. It was found that all the herds affected had been fed with brewers' grains supplied from a common source; and on examining microscopically a sample of these grains, they were seen to be swarming with the deadly bacillus, which, when it has once found its way among them, grows and multiplies with extraordinary rapidity.

The next important step in this investigation, was the discovery of the modification in the potency of the poison, which can be produced by the cultivation of this bacillus. Everyone knows that some of our most valued esculent plants and fruits are the cultured' varieties of types which man would scarcely care to use in their original state, on account of the unpleasantness of their flavour or their semi-poisonous qualities. And now that we know that these disease-germs are really humble types of vegetation, the idea naturally suggests itself whether they too may not be so far modified by the environment' in the midst of which they are developed, as to undergo some analogous modification. Two modes of such culture suggest themselves :--the introduction of the germs into the circulating current of animals of a different type, and its repeated transmission from one such animal to another ;--and cultivation carried on out of the living body, in fluids (such as blood-serum or meat-juice) which are found favourable to its growth, the temperature of the fluid in the latter case being kept up nearly to blood-heat. Both these methods have been used by Pasteur himself and by Professor Burdon Sanderson ; and the latter especially by M. Toussaint of Toulouse, who, as well as Pasteur, has experimented also on another bacillus which he had found to be the disease-germ of a malady termed' fowl cholera,' which proves very fatal among poultry in France and Swit

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zerland. It has been by Pasteur that the conditions of the mitigation of the poison by culture have been most completely determined ; so that the disease produced by the inoculation of his cultivated virus may be rendered so trivial as to be scarcely worth notice. His method consists in cultivating the bacillus in meat-juice or chicken broth, to which access of air is permitted while dust is excluded; and then allowing a certain time to elapse before it is made use of in inoculation experiments. If the period does not exceed two months, the potency of the bacillus seems but little diminished; but if the interval be extended to three or four months, it is found that though animals inoculated with the organism take the disease, they have it in a milder form, and a considerable proportion recover; whilst, if the time be still further prolonged, say to eight months, the disease produced by it is so mild as not to be at all serious, the inoculated animals speedily regaining perfect health and vigour.

Thus, then, it becomes possible to affect sheep and cattle with a form of anthrax-disease so mild, as to bear much the same relation to the severer forms that cow-pox bears to small-pox; and for this artificial affection with the mitigated disorder, Pasteur uses the term

vaccination. The question that now arises—to which the whole previous investigation has led up-is the most important of all : Does this vaccination with the mild virus afford the same protection against the action of the severe, that is imparted by cow-pox vaccination against amall-pox? To this question affirmative answers were last year obtained by Prof. Greenfield (on Prof. Burdon Sanderson's suggestion) in regard to bovine animals, and by M. Toussaint in regard to sheep and dogs; the former, when vaccinated' from rodents, and the latter from fluids cultivated' outside the living body after a method devised by M. Toussaint, proving themselves incapable of being infected with any form of anthrax-disease, though repeatedly inoculated with the malignant virus; and remaining free from all disorder, either constitutional or local. The same result having been obtained from experiments made by Pasteur bimself, probably about the same date, with charbon-virus cultivated in the manner previously described, it was deemed expedient by one of the Provincial Agricultural Societies of France, that this important discovery should be publicly demonstrated on a great scale. Accordingly, a farm and a flock of fifty sheep having been placed at M. Pasteur's disposal, he' vaccinated’ twenty-five of the flock (distinguished by a perforation of their ears) with the mild virus on the 3rd of May last, and repeated the operation on the 17th of the same month. The animals all passed through a slight indisposition ; but at the end of the month none of them were found to have lost either fat, appetite, or liveliness. On the 31st of that month, all the fifty sheep, without distinction, were inoculated with the strongest charbon-virus ; and M. Pasteur predicted that on the following day the twenty-five sheep inoculated for the first time would all be dead, whilst those protected by previous vaccination with the mild virus would be perfectly free from even slight indisposition. A large assemblage of agricultural authorities, cavalry officers, and veterinary surgeons having met at the field the next afternoon (June 1), the result was found to be exactly in accordance with M. Pasteur's predictions. At 2 o'clock twenty-three of the “unprotected' sheep were dead; the twenty-fourth died within another hour, and the twenty-fifth an hour afterwards. But the twenty-five vaccinated' sheep were all in perfectly good condition ; one of them, which had been designedly inoculated with an extra dose of the poison, having been slightly indisposed for a few hours, but having then recovered. The twentyfive carcases were then buried in a selected spot, with a view to the further experimental testing of the poisonous effect produced upon the grass which will grow over their graves. But the result, says the reporter of the Times (June 2), “is already certain ; and the agricultural public now know that an infallible preventive exists against the charbon-poison, which is neither costly nor difficult, as a single man can inoculate a thousand sheep in a day.'—I have since learned that this protection is being eagerly sought by the French owners of flocks and herds; and if any severe epidemic of the same kind were to break out in this country, our own agriculturists would probably show themselves quite ready to avail themselves of it. To the wool-sorters' of Bradford it must prove a most important boon, if they can be led to understand its value.

: I have seen notices of its serious prevalence during this very summer in some of the localities most frequented by tourists.

* It is not a little curious that as culture of one kind can mitigate the action of the poison germs, so culture of another kind may restore, or even increase, their original potency. It has been found by Pasteur that this may be effected by inoculating with the mitigated virus a new-born guinea-pig, to which it will prove fatal; then using its blood for the inoculation of a somewhat older animal; and repeating this process several times. In this way a most powerful virus may be obtained at will--a dis. covery not only practically valuable for experimental purposes, but of great scientific interest, as throwing light upon the mode in which mild types of other diseases may be converted into malignant. By Dr. Grawitz, indeed, it has been recently asserted that even some of the most innocent of our domestic microphytes may be changed by artificial culture into disease-germs of deadly infectiveness.

That this is not to remain an isolated fact, but will be the first of a series of discoveries of surpassing importance (some of them already approaching maturity), is shown by the fact that Pasteur has found himself able to impart a like protection against fowl-cholera, by • vaccinating' chickens with its cultivated bacillus.

These wonderful results obviously hold out an almost sure hope of preventing the ravages, not merely of the destructive animal plagues that show themselves from time to time among us, but of doing that for some of the most fatal forms of human infectious disease, which Jennerian vaccination has already done-as shown by Sir Thomas

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