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. Wine is sometimes 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 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. 
