FERMENTATION 303 



long known that mere exposure to the air was sufficient 

 to destroy it. Pasteur studied all these changes, traced 

 them to their living causes, and showed that the perma- 

 nent health of the vinegar was insured by the destruction 

 of this life. He passed from the diseases of vinegar to the 

 study of a malady which a dozen years ago had all but 

 ruined the silk husbandry of France. This plague, which 

 received the name of pebrine, was the product of a parasite 

 which first took possession of the intestinal canal of the 

 silkworm, spread throughout its body, and filled the sack 

 which ought to contain the viscid matter of the silk. Thus 

 smitten, the worm would go automatically through the 

 process of spinning when it had nothing to spin. Pasteur 

 followed this parasitic destroyer from year to year, and 

 led by his singular power of combining facts with the logic 

 of facts, discovered eventually the precise phase in the de- 

 velopment of the insect when the disease which assailed 

 it could with certainty be stamped out. Pasteur' s devo- 

 tion to this inquiry cost him dear. He restored to France 

 her silk husbandry, rescued thousands of her population 

 from ruin, set the looms of Italy ulso to work, but emerged 

 from his labors with one of his sides permanently para- 

 lyzed. His last investigation is embodied in a work en- 

 titled " Studies on Beer," in which he describes a method 

 of rendering beer permanently unchangeable. That method 

 is not so simple as those found effectual with wine and 

 vinegar, but the principles which it involves are sure to 

 receive extensive application at some future day. 



There are other reflections connected with this subject 

 which, even were they now passed over without remark, 

 would sooner or later occur to every thoughtful mind in 

 this assembly. I have spoken of the floating dust of the 



