or a little alkalin, and if I put it, furthermore, not in
one of your ovens where it is not sufficiently hot, but at
50◦ C., this same flask of urine which remains sterile in
your hands, becomes clouded at the end of 9 or 10 hours
and swarms with bacteria. From whence can they
come, if not from a spontaneous generation?"

Repeated immediately in the laboratory of Pasteur,
the experiment was successful. It is, in reality, very
exact, but what must we conclude from it? Pasteur
could not interpret it as Bastian did. He acknowledged
that the germs were there: but whence did they come?
In this investigation, Pasteur beat about the bush for a
long time, and during this time his ideas, like his discus-
sion with Bastian, were rather confused. I will simplify
my exposition considerably by saying that these germs
for which Pasteur demanded an explanation from ex-
perimentation, could be derived from three sources,
unsuspected up to that time: first from the solution of
potash; second from the boiled urine; and third from the
walls of the flask. It was, we see, the introduction of
solids and liquids, as conveyors of germs, into a question
where up to that time, the air, chiefly, had been incrimi-
nated. Let us examine separately the three sources
which we have just enumerated.

The solution of boiled potash may contain germs, and
yet that seems surprising when one thinks that this
solution is made with a piece of fused potash which, in a
solid state, actively attacks animal membranes and
destroys everything living. Therefore, it is not this
which can carry the germs, and, in reality, if we repeat
the experiment of Bastian, replacing the solution of boiled
potash with an equivalent fragment of fused potash,
the experiment does not succeed, and the urine con-
tinues to be sterile. Then it is the water that conveys
the germs, and in studying this subject Pasteur and

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