ON DUST AND DISEASE. 139 



Parasitic Diseases of Silkworms. Pasteur's 

 Researches. 



It is admitted on all hands that some diseases are 

 the product of parasitic growth. Both in man and in 

 lower creatures, the existence cf such diseases has been 

 demonstrated. I ain enabled to lay before you an ac- 

 count of an epidemic of this kind, thoroughly investi- 

 gated and successfully combated by M. Pasteur. For 

 fifteen years a plague had raged among the silkworms 

 of France. They had sickened and died in multitudes, 

 while those that succeeded in spinning their cocoons 

 furnished only a fraction of the normal quantity of silk. 

 In 1853 the silk culture of France produced a revenue 

 of one hundred and thirty millions of francs. During 

 the twenty previous years the revenue had doubled it- 

 self, and no doubt was entertained as to its further 

 augmentation. The weight of the cocoons produced in 

 1853 was 26,000,000 kilogrammes; in 1865 it had 

 fallen to 4,000,000, the fall entailing, in a single year, 

 a loss of 100,000,000 francs. 



The country chiefly smitten by this calamity hap- 

 pened 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 cir- 

 cumstances rendered almost personal, to undertake the 

 investigation of the malady. Pasteur at this time had 

 never seen a silkworm, and he urged his inexperience 

 in reply to his friend. But Dumas knew too well the 

 qualities needed for such an enquiry to accept Pasteur's 

 reason for declining it. ' Je mets,' said he, ' un prix 

 extreme a voir votre attention nxee sur la question qui 

 interesse mon pauvre pays ; la misere surpasse tout ce 



