288 FRAGMENTS OF SCIENCE. 



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 

 fixee sur la question qui interesse 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, 



