42 
M. PASTEUR. 
of life ; but he said in his Treatise of Organic Chemistry that 
this was only a deceiving mirage. 
All the experiments that I have made for the last twenty- 
three years have tended, directly or indirectly, to show the inex¬ 
actitude of the opinions of Liebig. From the beginning, that is 
about 1857, a method almost unique has served me as a guide in the 
study of microscopical organisms, it consists essentially in the 
culture of these little beings in their pure, original condition, un¬ 
affected by any of the heterogenous matters, living or dead, which 
accompany them. In using this method, the most difficult ques¬ 
tions sometimes receive easy and definitive solutions. I will re¬ 
call one of the first applications I made of it: Ferments, said 
Liebig, are all those nitrogenous compounds of the organism, fibrin, 
albumen, caseine, * * * in the state of alteration that they 
undergo by the effect of the contact of air. Fermentation, in 
fact, is not known where such compounds are not present and 
active. Spontaneity was claimed all over as the originating cause 
of the inception and march of fermentation as in those of dis¬ 
eases. In order to demonstrate that the theory of the learned 
German chemist was, to use his own words, only a “ deceiving 
mirage,” I employed artificial media, containing only pure water, 
witli the mineral substances necessary to life, fermentable mat¬ 
ters and the germs of ferments of those different matters. In 
those conditions, fermentations took place with a regularity and a 
purity, if I may so say, which did not always exist in the natural 
spontaneous fermentations. All albumenoid substances being left 
aside, fermentation developed as a living being, which borrowed 
from the fermentible elements all the carbon of its successive 
generations and from the mineral medium the nitrogen, phos¬ 
phorus, potassium, magnesium, elements whose assimilation is one 
of the necessary conditions of the formation of all beings, great 
or small. 
Thus, not only was the theory of Liebig proved without 
foundation, but the phenomena of fermentations presented them¬ 
selves as simple phenomena of nutrition, taking place in excep¬ 
tional conditions, amongst which the most strange and significant 
no doubt, is the possible absence of the contact of air. Human 
