As all these belonged to the experiments under way,
an attempt was made to revive them, and with that
end in view, transfers were made from them either into
chicken bouillon or into chickens. Many of these made
no growth, and also spared and left unimpaired the
animals into which they were inoculated, and we were
about to throw them away, in order to begin anew, when
it occurred to Pasteur to inoculate a fresh young culture
into these chickens which, at least in appearance, had
so well resisted the inoculations with the cultures
made the preceding summer.

To the surprise of all, perhaps even of Pasteur him-
self, who did not expect such a success, almost all of these
chickens resisted, whereas new chickens, just brought
from the market, succumbed in the ordinary length of
time, thus showing that the culture used for the inocu-
lation was very active. With one blow, chicken cholera
passed to the list of virus diseases and vaccination was
discovered! What secret instinct, what spirit of divin-
ation impelled Pasteur to knock at this door, which
was only waiting to be opened? Here we see clearly
the part played by his readings and his former studies,
by the incessant ponderings which had been going on
in his mind, and by the intervention, in the midst of
three obscurities, of this faculty of imagination to which
he has referred in the lines that precede, lines written
just at the time when he was setting forth, a conqueror,
in the realm of his dream.

He had, in reality, just established between certain
microbial diseases and the virus diseases a definite
connection which it was to be the task of the future
to enlarge and consolidate. There were, then, microbial
diseases which did not recur! One could, therefore,
prepare vaccines insuring protection against a viru-
lent inoculation! Prudently, Pasteur refrained from

-281-