Fifty sheep in a yard proved that the vaccine worked on fifty sheep in a yard. Whether it worked on the flocks of France was a different question, answered by a different instrument: the counts that farmers, veterinarians and Pasteur’s own laboratory kept over the next two years. This piece follows those counts as Pasteur laid them before the agricultural societies and the Académie, and the failures that his critics laid beside them. The French is my translation.

The first summer

The method, Pasteur told the International Medical Congress in London in August 1881, “had scarcely become known before it passed into large-scale practice.” Farmers wrote to the rue d’Ulm for vaccine, and the laboratory could not make it fast enough: in fifteen days, he said, nearly 20,000 sheep had been vaccinated in the departments round Paris, with a great many cattle and horses. The first repetition of the trial was at the farm of Lambert, near Chartres, in the Beauce, the great sheep country south-west of Paris, where a commission of doctors, surgeons and veterinarians took the view that a laboratory culture was a laboratory thing and that the real test was the blood of a dead animal. On 16 July, Vallery-Radot says, sixteen Beauce sheep and nineteen vaccinated sheep from the Alfort school were inoculated with the blood of a sheep that had died of anthrax four hours before, on a neighbouring farm. “The result was that of Pouilly-le-Fort,” Pasteur told London: absolute resistance of the vaccinated, death of the unvaccinated.

In the Brie, at Noyen, Roux vaccinated 993 sheep on 8 and 18 August 1881 and left 728 unvaccinated; by 5 January 1882 seventeen of the unvaccinated had died of anthrax and none of the vaccinated. At Rozières, on the farm of a M. Gatté, half a flock of 500 was vaccinated by 8 July, and from 15 to 29 August the whole flock was folded on a field known to be dangerous; eight unvaccinated sheep died there and no vaccinated one. On 5 December six unvaccinated and twelve vaccinated sheep of the same farm were inoculated with anthrax blood; the six were dead by the morning of the 9th and none of the twelve was ill.

The figures at Melun

On 26 January 1882 the Société d’agriculture de Melun held its annual meeting with Pasteur as its guest. Before it, in a courtyard of the town hall, he and his assistants challenged twenty-three sheep with virulent culture: some had been vaccinated and challenged at Pouilly-le-Fort in May, some had had only the vaccine, some nothing. By 31 January the unvaccinated were all dead and the others well and eating. The immunity given in May had lasted at least eight months, and that, he told the Société nationale d’agriculture in February, settled the practical question: vaccinate in April and the flock is safe for the season, which runs from April to October. The president of the Melun society gave him three medals, in bronze, silver and gold, with his portrait on one face and the date of the trial on the other, and Pasteur gave the society the ledger of the summer.

From July to September 1881, 32,550 sheep had been vaccinated and 25,100 left as controls beside them. “From vaccination to the end of October, ten times more unvaccinated sheep died than vaccinated.” Of 138 flocks, forty-five, with 10,500 sheep, had lost no vaccinated animal during or after vaccination. In fifteen flocks where anthrax had been killing before the vaccinators came, 2,867 unvaccinated sheep lost 141 in two months and 3,003 vaccinated lost none, where 180 might have been expected. During the vaccinations themselves, sixty unvaccinated and fifty-eight vaccinated sheep had died, “as if the first vaccination had already preserved a certain number.” Of cattle, 1,254 had been vaccinated and 888 left: one vaccinated cow and ten unvaccinated had died in the two months after. Of horses, 142 vaccinated and eighty-odd left: one horse died of septicaemia during vaccination, and no other. From November to January, 42,000 more sheep and 7,500 cattle and horses: about 200 sheep had died during vaccination, “whether by continuation of the mortality that existed in the flocks before vaccination, or by circumstances that may be attributed to accidents of vaccination”; three cows in 7,000; two horses in 500. In February he put the whole at more than 90,000 animals, 80,000 of them sheep.

The failures

Not every yard was Pouilly-le-Fort, and Pasteur said so, after a fashion, on 9 April 1883, in a note to the Académie occasioned by a failure at Turin. Most of the repetitions of the trial abroad and in France, he said, had succeeded as the original had; “some others failed more or less,” the virulent dose killing not only the controls but a variable number of the vaccinated, “whether there was some fault of handling, or the vaccine itself was too weak against the virulent virus, or by susceptibility of breed, or finally because the experimenters had indulged in certain innovations the experiment did not allow, for instance replacing sheep by guinea pigs or rabbits.” The Turin failure, in March 1882, had killed every sheep, vaccinated or not. Pasteur wrote to the school on 16 April to ask when the sheep whose blood had been used had died, learned it was the morning before, and told the central veterinary society on 8 June that the Italians had inoculated, without knowing it, a blood that was septic as well as anthracic. Six professors of Turin answered together that they found it marvellous that his illustrious lordship could tell from Paris what had been in their syringe.

The weightier critic was Robert Koch, whose discovery of the spore in 1876 had made the whole subject, and who with his assistants at the Imperial Health Office in Berlin repeated the attenuations, found the vaccines inconstant and the statistics unconvincing, and said so in print in 1882. Pasteur answered at the international congress at Geneva in September 1882 and in a published reply, in which he set the test that had been passed “at Pouilly-le-Fort, at Packisch, at Kapuvar and so many other places” against the test nobody would dare to make with Jenner’s vaccine: “would you dare, after vaccinating a hundred children, to inoculate them with the virus of black smallpox?” In June 1882 a veterinarian named Weber laid some accidents before the central veterinary society; Pasteur replied that about 45,000 vaccinations had been made between the end of June and September 1881 without any being reported, and that two vaccinated sheep of M. Gatté’s flock had died of anthrax on 25 May and 3 June 1882, a year after their vaccination, the rest of the flock resisting.

Eure-et-Loir

The best count was made by the people with the most to lose. Eure-et-Loir, the department of Chartres, was the one anthrax hit hardest, and in 1882 its veterinarians vaccinated nearly 80,000 sheep, 4,000 to 5,000 cattle and 500 horses. The veterinary and agricultural society of Chartres collected the results and had them read by Ernest Boutet, a veterinarian of the town, on 29 October 1882; Pasteur laid the conclusions before the Académie on 18 December. The number of sheep vaccinated in the year was 79,392. In those flocks the average annual loss over the previous ten years had been 7,237 sheep, or 9.01 per cent. Since vaccination, 518 had died of anthrax, or 0.65 per cent. The year had been a mild one, Boutet allowed, with losses in the department of about three per cent; even so the flocks should have lost 2,382 and had lost 518. In flocks vaccinated only in part, 2,308 vaccinated sheep had lost eight, or 0.4 per cent, and 1,659 unvaccinated had lost sixty, or 3.9 per cent, “subject to the same conditions of soil, housing, food and temperature.”

That is the figure to put beside the fifty sheep. The yard had shown a difference of twenty-five to nothing in two days; the department showed a difference of about ten to one over a year, in flocks nobody had marked with a hole in the ear. The second is the result that mattered to the farmers, and it was the one the laboratory’s own ledger, kept in the rue Vauquelin where Chamberland made the vaccine and sold it, had been predicting since the first summer.

Sources

• Louis Pasteur, the London address of August 1881; the speech at Melun of 26 January 1882; the note to the Société nationale d’agriculture of February 1882; the reply to Weber of 8 June 1882; the Eure-et-Loir statistics of 18 December 1882; “Sur la vaccination charbonneuse” of 9 April 1883; and the reply to Koch. All in the Œuvres de Pasteur, volume VI (Paris, 1933), pages 370–444. The French: “Depuis la vaccination jusqu’à la fin d’octobre, il est mort dix fois plus de moutons non vaccinés que de vaccinés”; “comme si la première vaccination avait déjà préservé un certain nombre d’animaux”; “soit par continuation de la mortalité qui existait dans les troupeaux avant la vaccination, soit par des circonstances qu’on peut attribuer à des accidents de vaccination”; “Quelques autres échouèrent plus ou moins”; “soit qu’il y eût quelque vice de manipulation, soit que le vaccin lui-même eût été trop faible vis-à-vis du virus virulent, soit par réceptivité de races, soit enfin que les expérimentateurs se fussent livrés à certaines innovations que l’expérience ne comportait pas, par exemple, le remplacement des moutons par des cobayes ou des lapins”; “à Pouilly-le-Fort, à Packisch, à Kapuvar et tant d’autres lieux”; “Oseriez-vous, après avoir vacciné cent enfants, les inoculer par le virus de la variole noire?”; “les moutons vaccinés et non vaccinés sont soumis aux mêmes conditions de sol, de logement, de nourriture, de température.” archive.org
• René Vallery-Radot, La vie de Pasteur (Paris, 1900), for the Lambert farm on 16 July 1881 and the Turin exchange of 1882. archive.org
• Louis Pasteur, “Sur la vaccination charbonneuse,” Comptes rendus 96 (9 April 1883), 979 onward, in the same issue as Chamberland and Roux’s note on antiseptics. archive.org
• Gerald L. Geison, The Private Science of Louis Pasteur (Princeton University Press, 1995), chapter 6, for the annexe in the rue Vauquelin, the sale of the vaccine, and Koch’s criticism. In copyright. press.princeton.edu