DUST AND DISEASE. -280 



from sugar to sulphate of quinine — all lias been invoked in 

 behalf of this unhappy insect." The helpless cultivators, 

 moreover, welcomed with ready trustfulness every new 

 remedy, if only pressed upon them with sufficient hardi- 

 hood. It seemed impossible to diminish their blind confi- 

 dence in their blind guides. In 1863 the French Minister 

 of Agriculture himself signed an agreement to pay 500,000 

 francs for the use of a remedy which its promoter declared 

 to be infallible. It was tried in twelve different depart- 

 ments of France, and found perfectly useless. In no single 

 instance was it successful. It was under these circum- 

 stances that M. Pasteur, yielding to the entreaties of his 

 friend, betook himself to Alais in the beginning of June, 

 18G5. As regards silk husbandry, this was the most im- 

 portant department in France, and it was also that which 

 had been most sorely smitten by the epidemic. 



The silk-worm had been previously attacked by mus- 

 cardlne, a disease proved by Bassi to be caused by a vege- 

 table parasite. Though not hereditary, this malady was 

 propagated annually by the parasitic spores, which, wafted 

 by winds, often sowed the disease in places far removed 

 from the centre of infection. Muscardine is now said to 

 be very rare ; but for the last fifteen or twenty years a 

 deadlier malady has taken its place. A frequent outward 

 sign of this new disease are the black spots which cover 

 the silk-worms, hence the name pebrine, first applied to 

 the plague by M. de Quatrefages, and adopted by Pasteur. 

 Pebrine declares itself in the stunted and unequal grow r th 

 of the worms, in the languor of their movements, in their 

 fastidiousness as regards food, and in their premature 

 death. The track of discovery as regards the epidemic 

 is this: In 1849 Guerin Mcmeville noticed in the blood 

 of silk- worms vibratory corpuscles which he supposed to 

 be endowed with independent life. Filippi proved him 

 wrong, and showed that the motion of the corpuscles was 



