80 PASTEUR: THE HISTORY OF A MIND 



But, while keeping them separate, we can make these 

 fermentations follow each other, although, according to 

 the ideas of Liebig, they are interblended. Take this 

 liquid in which the lactic ferment has grown, and in 

 which there are only lactate of lime and mineral salts 

 in solution: after having heated it to sterilize it, sow 

 there a drop of a liquid in which there has occurred 

 spontaneously a butyric fermentation, and, therefore, 

 one which is almost surely impure. Phenomena anal- 

 ogous to those of alcoholic fermentation occur: a gas is 

 liberated which is no longer a pure carbonic acid, but a 

 mixture of this gas and hydrogen. This mixture has 

 very little odor, because of the absence of sulphuretted 

 hydrogen. These are the indications of a fermentation. 

 Let us see now what is present in the liquid which has 

 become clouded. We find there only motile rods, very 

 agile, with undulating movements, sometimes ranged in 

 a series, like a string of boats, and then motile on their 

 articulations (Fig. 8, sec. 3), which testifies to the fact 

 that they reproduce and multiply by elongating and 

 segmenting across their longer axis; this is the mode of 

 reproduction called fission. 



When he observed for the first time those organisms 

 which he called vibrios, Pasteur had a great surprise, 

 the trace of which is visible in his note on this subject. 

 The yeast of beer and the lactic ferment were non-motile 

 globules; the butyric ferment was motile, and partook 

 of the nature [animal] of those organisms which Ehren- 

 burg and Dujardin had found in infusions. O the power 

 of words! Nothing was more natural than to find in 

 fermentations the same organisms as in infusions, since 

 Pasteur nourished his ferments with vegetable infusions; 

 he hesitates, however, on finding that the butyric ferment 

 belongs to the Infusoria. "I was so far, " he said, "from 

 expecting such a result, so far, indeed, that for a long 



