258 FRAGMENTS OF SCIENCE. 



this experiment ? Obviously that the particles adherent 

 to the external surface of the grape include the germs 

 of that life which, after they have heen sown in the 

 juice, appears in such profusion. Wine is sometimes 

 objected to on the ground that fermentation is ' arti- 

 ficial ; ' but we notice here the responsibility of nature. 

 The ferment of the grape clings like a parasite to the 

 surface of the grape ; and the art of the wine-maker 

 from time immemorial has consisted in bringing- and 

 it may be added, ignorantly bringing two things thus 

 closely associated by nature into actual contact with 

 each other. For thousands of years, what has been 

 done consciously by the brewer, has been done uncon- 

 sciously by the wine-grower. The one has sown his 

 leaven just as much as the other. 



Nor is it necessary to impregnate the beer-wort 

 with yeast to provoke fermentation. Abandoned to 

 the contact of our common air, it sooner or later 

 ferments; but the chances are that the produce of that 

 fermentation, instead of being agreeable, would be 

 disgusting to the taste. By a rare accident we might 

 get the true alcoholic fermentation, but the odds 

 against obtaining it would be enormous. Pure air 

 acting upon a lifeless liquid will never provoke fer- 

 mentation ; but our ordinary air is the vehicle of 

 numberless germs which act as ferments when they fall 

 into appropriate infusions. Some of them produce 

 acidity, some putrefaction. The germs of our yeast- 

 plant are also in the air ; but so sparingly distributed 

 that an infusion like beer-wort, exposed to the air, is 

 almost sure to be taken possession of by foreign 

 organisms. In fact, the maladies of beer are wholly 

 due to the admixture of these objectionable ferments, 

 whose forms and modes of nutrition differ materially 

 from those of the true leaven. 



