282 PASTEUR : THE HISTORY OF A MIND 



sayijig how he obtained this vaccine. He preferred to 

 insert in the Note in which he announced the preceding 

 fact, another fact not less astonishing, to wit, that this 

 vaccine, once developed, could be reproduced indefinitely 

 by cultures, with all its vaccinal properties, or with what 

 has since been called its degree of attenuation. 



If one can say, strictly speaking, that Pasteur had 

 had a presentiment of the first of these facts, the latter 

 at least was entirely unforeseen. It is, or seems to us 

 at least, entirely independent of the other, and it is 

 possible that vaccination would still be in force even 

 if the latter did not exist. But it was none the less 

 valuable in practice, and Pasteur in running across it 

 must have recalled the history of Jenner, and even 

 have re-lived it. And here is my reason! 



It is well known that Jenner, after having discovered 

 that inoculation with cowpox gave protection against 

 smallpox and became a vaccine, had had some anxiety 

 regarding it. He feared, in the first place, being obhged to 

 return to the cow and to the cowpox to obtain his vaccine, 

 and this prospect was scarcely calculated to please 

 him. According to his idea, cowpox was inoculated 

 into the cow by a milker affected with smallpox, was 

 found only in the female and at the points touched by 

 the milker, that is on the udder, and represented con- 

 sequently the bovine form of human smallpox. If this 

 were so, there must be smallpox in order to produce 

 cowpox, and as, theoretically, the vaccine suppressed 

 the smallpox, here was a vicious circle. Jenner sought, 

 therefore, with an emotion of which we find traces in 

 his memoirs, to obtain from man the material for inocu- 

 lation, the vaccine, to vaccinate from arm to arm, and 

 he succeeded. It was his chief discovery, and one which 

 makes for his eternal glory. But the same history 

 repeated itself in Pasteur nearly a century later and 



