becomes populated just as if the neck had been broken
off. Another proof is this: when the neck is removed
one often sees ( Fig. 12 ) the first development of growth
directly under the opening, where the germs from the air
have fallen in."

"I am not content," Pasteur might have continued,
condensing his powerful argument, "I am not content
with giving you convincing experiments which always
succeed. I do more than that. I explain why my
predecessors have so often obtained those contradictory
results which have troubled them and stayed their
decisions. Thus, always, Schwann and the others have
seen their best-contrived experiments fail when they
placed their liquids, if only for an instant, in contact
with mercury. What imprudence! Is not the mercury
constantly and necessarily full of impurities? Those
particles of dust which come to it from the air, and
which collect on its surface, mingle with it and are
carried along with it everywhere. It is for this reason
that I have carefully excluded it from all the preceding
experiments, which, performed with its aid, might have
been easier to carry out, but which might have left us
uncertain as to the results.

"And then, to disturb our convictions, there is also the
history of this milk which curdles or putrefies under
conditions where beef bouillon, the must of beer, and
other infusions remain unaltered. There is this yolk of
egg, or this meat without water, which we cannot pre-
serve by heating to 100° C. and keeping afterwards in

-100-