88 THE POPULAR SCIENCE MONTHLY. 



gas, from all contact with air. The butyric ferment not only lives 

 without air, hut Pasteur showed that air is fatal to it. He finally di- 

 vided microscopic organisms into two great classes, which he named 

 respectively cerobies and ancerobies, the former requiring free oxygen 

 to maintain life, the latter capable of living without free oxygen, but 

 able to wrest this element from its combinations with other elements. 

 This destruction of pre-existing compounds and formation of new ones, 

 caused by the increase and multiplication of the organism, constitute 

 the process of fermentation. 



Under this head are also rightly ranked the phenomena of putre- 

 faction. As M. Radot well expresses it, the fermentation of sugar 

 may be described as the putrefaction of sugar. In this particular field 

 M. Pasteur, whose contributions to the subject are of the highest value, 

 was preceded by Schwann, a man of great merit, of whom the world 

 has heard too little.* Schwann placed decoctions of meat in flasks, 

 sterilized the decoctions by boiling, and then supplied them with cal- 

 cined air, the power of which to support life he showed to be unim- 

 paired. Under these circumstances putrefaction never set in. Hence 

 the conclusion of Schwann, that putrefaction was not due to the con- 

 tact of air, as affirmed by Gay-Lussac, but to something suspended 

 in the air which heat was able to destroy. This something consists of 

 living organisms which nourish themselves at the expense of the or- 

 ganic substance, and cause its putrefaction. 



The grasp of Pasteur on this class of subjects was embracing. He 

 studied acetic fermentation, and found it to be the work of a minute 

 fungus, the mycoderma aceti, which, requiring free oxygen for its 

 nutrition, overspreads the surface of the fermenting liquid. By the 

 alcoholic ferment the sugar of the grape-juice is transformed into car- 

 bonic-acid gas and alcohol, the former exhaling, the latter remaining 

 in the wine. By the mycoderma accti, the wine is, in its turn, convert- 

 ed into vinegar. Of the experiments made in connection with this 

 subject one deserves especial mention. It is that in which Pasteur 

 suppressed all albuminous matters, and carried on the fermentation 

 with purely crystallizable substances. He studied the deterioration of 

 vinegar, revealed its cause, and the means of preventing it. He de- 

 fined the part played by the little eel-like organisms which sometimes 

 swarm in vinegar-casks, and ended by introducing important ameliora- 

 tions and improvements in the manufacture of vinegar. The discussion 

 with Liebig and other minor discussions of a similar nature, which M. 

 Radot has somewhat strongly emphasized, I will not here dwell upon. 



It was impossible for an inquirer like Pasteur to evade the ques- 

 tion, Whence come these minute organisms which are demonstrably 

 capable of producing effects on which vast industries are built and on 

 which whole populations depend for occupation and sustenance ? He 

 thus found himself face to face with the question of spontaneous genera- 



* It was late in the day when the Royal Society made him a foreign member. 



