i 3 4 THE POPULAR SCIENCE MONTHLY. 



who, however keen and clever as observers, are not rigidly-trained ex- 

 perimenters. These alone are aware of the precautions necessary in 

 investigations of this delicate kind. In reference, then, to the life of 

 the wine-vat, what is the decision of experiment when carried out by 

 competent men ? Let a quantity of the clear, filtered " must " of the 

 grape be boiled, so as to destroy such germs as it may have contracted 

 from the air or otherwise. In contact with germless air the uncon- 

 taminated must never ferments. All the materials for spontaneous 

 generation are there, but so long as there is no seed sown there is no 

 life developed, and no sign of that fermentation which is the concomi- 

 tant of life. Nor need you resort to a boiled liquid. The grape is 

 sealed by 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 ac- 

 quires the power to ferment itself, nor to produce fermentation in 

 other liquids. 1 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 confidence : At the time 

 of the vintage little 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 ren- 

 dered turbid by the dust. Examined by a microscope, these minute 

 particles are seen to present the appearance of organized cells. In- 

 stead 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 fermenta- 

 tion. "What is the inference to be drawn from this experiment ? Ob- 

 viously that the particles adherent to the external surface of the 

 grape are the veritable germs of that life which, after they have been 

 sown in the juice, ajjpears in such profusion. Wine is sometimes ob- 

 jected to on the ground that fermentation is "artificial;" but we no- 

 tice here the responsibility of Nature. The ferment of the grape is 

 in fact a parasite 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 unconscious- 

 ly 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 leaven to 

 provoke fermentation. Abandoned to the contact of our common air, 



1 The liquids of the healthy animal body are also sealed from external contamination. 

 Neither pure urine, collected fresh from the bladder, nor pure blood, drawn with due 

 precautions from the veins, will ever putrefy in contact with pure air. 



