258 FKAGMENTS OF SCIENCE. 



mentation. What is the inference to be drawn from 

 this experiment? Obviously that the particles adher- 

 ent 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 some- 

 times objected to on the ground that fermentation is 

 ' artificial; ' but we notice here the responsibility of 

 nature. The ferment of the grape clings like a para- 

 site 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 unconsciously 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 fer- 

 ments; but the chances are that the produce of that 

 fermentation, instead of being agreeable, would be dis- 

 gusting 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 iipon 

 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 ob- 

 jectionable ferments, whose forms and modes of nu- 

 trition differ materially from those of the true leaven. 



