FERMENTATION. 537 



its own skin against contamination from without. By an 

 ingenious device Pasteur has extracted from the interior of 

 the grape its pure juice, and proved that in contact with 

 pure air it never acquires the power to ferment itself, nor 

 to produce fermentation in other liquids.* It is not 

 therefore, in the interior of the grape that the origin of 

 the life observed in the vat is to be sought. 



What then is its true origin? This is Pasteur's answer, 

 which his well-proved accuracy renders worthy of all con- 

 fidence. At the time of the vintage microscopic particles 

 are observed adherent, both to the outer surface of the 

 grape and of the twigs which support the grape. Brush 

 these particles into a capsule of pure water. It is rendered 

 turbid by the dust. Examined by a microscope, some of 

 these minute particles are seen to present the appearance 

 of organized cells. Instead of receiving them in water, 

 let them be brushed into the pure inert juice of the grape. 

 Forty-eight hours after this is done, our familiar Torula is 

 observed budding and sprouting, the growth of the plant 

 being accompanied by all the other signs of active fermen- 

 tation. What is the inference to be drawn from this ex- 

 periment? 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. AVine is sometimes objected to on the 



f round that fermentation is " artificial; " but we notice 

 ere 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 it is 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 



*The liquids of the healthy animal body are also sealed from ex- 

 ternal contamination. Pure blood, for example, drawn with due 

 precautions from the veins, will never ferment or putrefy in contact 

 with pure air. 



