Louis Pasteur (1822-1895) / by E.J. McWeeney.

  • McWeeney, Edmond J. (Edmond Joseph), 1864-1925.
Date:
[1912]
Catalogue details

Licence: In copyright

Credit: Louis Pasteur (1822-1895) / by E.J. McWeeney. Source: Wellcome Collection.

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    not be found. (Now, after the lapse of thirty years, we know why it was that Pasteur could not see this microbe, or grow it.) Not being able to cultivate the virus outside the body, Pasteur adopted the only means open to him—he grew it in the brain of living rabbits, transferring it from one that had just died to fresh animals. He noticed that the time that elapsed between inoculation and the outbreak of the symptoms gradually became shorter, until it was at last reduced to seven days. Pas¬ teur called this seven-day virus, virus fixe, because it took a fixed time to produce the disease, instead of the variable and inconstant periods taken by the virus procured from ordinary mad dogs as captured in the streets. This important progress made, Pasteur began to see his way to the final goal—that of immunization. Having found out how to intensify the virus, he now sought for a means of weakening it. The simplest possible plan was that which he had learnt by accident in the case of chicken-cholera, namely, the lapse of time. Accordingly he took the spinal cords of rabbits that had just died of virus fixe, suspended them by threads in flasks, the air in which was kept dry by a lump of caustic potash lying at the bottom, and kept them at a constant temperature for days. At intervals he tried the effect of inocu¬ lating rabbits with matter from these cords, and found that after a fortnight in the flask all virulence was lost. The shorter the period of drying, the greater the amount of virulence that was retained. Accordingly, Pasteur next proceeded to an immunization experiment. Into a number of dogs he injected first of all some spinal cord that had been kept a fortnight, next day some that had been kept thirteen days, and so on till he was giving them material from rabbits that had only died that very day—the redoubtable virus fixe. The dogs so treated remained well, and it was found that they could be bitten by mad companions or even intra-cranially inoculated 207
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