FERMENTS, FERMENTATIONS, AND LIFE. 265 
bunches have been subjected to constant rains. In this 
case, plainly, fermentation is due to the germs suspended 
in the air, or deposited on the surface of the grapes and 
stems. Pasteur draws blood from an animal’s veins by a 
similar process, and introduces it into a glass vessel in con- 
tact with pure air. The blood continues fresh for years. 
Pasteur asserts and proves by experiment that grape-juice, 
milk, blood, and all liquids that most readily undergo change 
in ordinary conditions, are incapable of fermentation in air 
which is pure, that is to say, deprived of the corpuscles it 
contained. They remain, when so placed, for an indefinite 
time, in a singularly sound state. 
Pasteur had made still another set of experiments. He 
had obtained development of fermentation in liquids freed 
from albuminoid substances. It was supposed, before his 
researches, that the cells remarked in the fermentation of 
grape-juice proceed from the conversion of the albuminoid 
substances which this fluid contains in its natural state. 
Pasteur prepares a solution of sugar, tartrate of ammonia, 
and some other salts, and sprinkles a few yeast-globules in 
it. They swell, develop, and propagate in this artificial 
‘medium quite as well as in the grape-juice. So it was sup- 
posed that in the acid fermentation of milk the ferment is a 
product of the conversion of casein. Pasteur proves that 
supposition to be unfounded, by artificially producing the 
lactic ferment in a compounded liquid containing not a 
trace of casein. These very delicate experiments have not 
only increased the vogue of the panspermic theory, but 
they have been of great value also to vegetable physiology. 
Many objections have been raised to these theories on 
the origin of ferments, to which Pasteur has almost always 
replied by unquestionable facts and solid reasonings, though 
he has sometimes done himself the injustice to be rough 
and contemptuous in discussion toward his opponents. 
Truth is strong enough to indulge charity for error. The 
