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 



