272 THE FLOATING-MATTER OF THE AIR. 



labours were based. Ravages had over and over again 

 occurred amono: French wines. There was no (guarantee 

 that they would not become acid or bitter, particularly 

 when exported. The commerce in wines was thus 

 restricted, and disastrous losses were often inflicted on 

 the wine-grower. Every one of these diseases was 

 traced to the life of an organism. Pasteur ascertained 

 the temperature which killed these ferments of disease, 

 proving it to be so low as to be perfectly harmless to- 

 the wine. By the simple expedient of heating the- 

 wine to a temperature of fifty degrees Centigrade, he 

 rendered it inalterable, and thus saved his country the 

 loss of millions. He then went on to vinegar — vin 

 aigre, acid wine — which he proved to be produced by 

 a fermentation set up by a little fungus called 

 Mycoderma aceti, Torula, in fact, converts the grape 

 juice into alcohol, and Mycoderma aceti converts the 

 alcohol into vinegar. Here also frequent failures 

 occurred, and severe losses were sustained. Through 

 the operation of unknown causes, the vinegar often 

 became imfit for use, sometimes indeed falling into utter 

 putridity. It had been 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 permanent health of the vinegar 

 was ensured 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 silk- 

 worm, 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* 



