flamed flasks, when he wishes to cultivate and keep pure
a species the condition for the development of which
he knows only imperfectly, Aspergillus niger gives
admirable cultures, flourishing and pure, in contact with
the air, and in liquids and flasks which one has not taken
the trouble to sterilize. Consequently, in the presence of
every new species, his first care was to try several culture
media so as to find that which suited it the best.

Having this principle of culture in the most favorable
medium, Pasteur was also the only one who had the
ability to add a proper technique. This was due especially,
as we have seen, to the efforts of his assistants: Joubert,
Chamberland and Roux.

Finally, as a last advantage, Pasteur had that of being
20 years old in the study of microbes and of having more
complete notions about them, their needs, their physi-
ology and their morphology, than any of the scientific
men of his time. It was because of this that he was
able so quickly to catch up with and soon to distance
those who had entered before him on this pathway,
for at the time when he first took up the study of anthrax
in 1876, there had been already several pathogenic mi-
crobes discovered, and Koch had just published his
famous work on the spore of the anthrax bacteridium.

To appreciate thoroughly the rôle and the part of
Pasteur in this great question of pathology, one must
know the general state of science and of the scientific
mind in 1876. ¹ That is not as easy as one might believe
it to be, considering that we have to go back only a few
years. The ideas which had currency in 1840 and even
in 1860 on the subject of contagious diseases are so far
removed from our own that they have almost the dis-

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