214 THE FLOATING-MATTER OF THE AIR. 



experiment? Obviously that the particles adherent 

 to the external surface of the grape include the germs 

 of that life which, after they have been 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 fermentation ; 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 putre- 

 faction. 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 mala- 

 dies 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. 



