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tures, the existence of such diseases has been demonstrated.
I am enabled to lay before you an account of an epidemic
of this kind, thoroughly investigated and successfully com-
batted by M. Pasteur. For fifteen years a plague had
raged among the silk-worms of France. They had sickened
and died in multitudes, while those that succeeded in Spin-
ning their cocoons furnished only a fraction of the normal
quantity of silk. In 1853 the silk culture of France pro-
duced a revenue of one hundred and thirty millions of
francs. During the twenty previous years the revenue had
doubled itself, and no doubt was entertained as to its future
augmentation. The weight of the cocoons produced in
1853 was twenty-six millions of kilogrammes; in 1865 it
had fallen to four millions, the fall entailing in the single
year last mentioned a loss of one hundred millions of francs.

The country chiefly smitten by this calamity happened
to be that of the celebrated chemist, Dumas, now perpetual
secretary of the French Academy of Sciences. He turned
to his friend, colleague, and pupil, Pasteur, and besought
him with an earnestness which the circumstances rendered
almost personal, to undertake the investigation of the
malady. Pasteur at this time had never seen a silk-worm,
and he urged his inexperience in reply to his friend. But
Dumas knew too well the qualities needed for such an in-
quiry to accept Pasteur’s reason for declining it. “ Je
mets,” said he, “un prix extreme a voir votre attention
fixée sur la question qui intéresse mon pauvre pays; la
misere surpasse tout ce que vous pouvez imaginer.”
Pamphlets about the plague had been showered upon the
public, the monotony of waste-paper being broken at rare
intervals by a more or less useful publication. “ The
Pharmacopoeia of the Silk-worm,” wrote M. Cornalia in
1860, “is now as complicated as. that of man. Gases,
liquids, and solids have been laid under contribution.
From chlorine to sulphurous acid, from nitric acid to rum,

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