348 , LOUIS PASTEUR 



On June 28th, fermentation was quite finished; there was 

 no longer any trace of gas, nor any lactate in solution. All 

 the infusoria were lying motionless at the bottom of the 

 flask. The liquid clarified by degrees, arid in the course of 

 a few days became quite bright. Here we may inquire, were 

 these motionless infusoria, which from complete exhaustion 

 of the lactate, the source of the carbonaceous part of their 

 food, were now lying inert at the bottom of the fermenting 

 vessel were they dead beyond the power of revival? 7 The 

 following experiment leads us to believe that they were not 

 perfectly lifeless, and that they might behave in the same 

 manner as the yeast of beer, which, after it has decomposed 

 all the sugar in a fermentable liquid is ready to revive and 

 multiply in a fresh saccharine medium. On April 22nd, 

 1875, we left in the oven at a temperature of 25 C. (77 F.) 

 a fermentation of lactate of lime that had been completed. 

 The delivery tube of the flask A, (FiG. 15), in which it had 

 taken place, had never been withdrawn from under the 

 mercury. We kept the liquid under observation daily, and 

 saw it gradually become brighter; this went on for fifteen 

 days. We then filled a similar flask, B, with the solution of 

 lactate, which we boiled, not only to kill the germs of 

 vibrios which the liquid might contain, but also to expel 

 the air that it held in solution. When the flask, B, had 

 cooled, we connected the two flasks, avoiding the introduc- 

 tion of air," after having slightly shaken the flask, A, to stir 

 up the deposit at the bottom. There was then a pressure 

 due to carbonic acid at the end of the delivery tube of this 

 latter flask, at the point a, so that on opening the taps r and 

 s, the deposit at the bottom of flask A was driven over into 

 flask B, which in consequence was impregnated with the 

 deposit of a fermentation that had been completed fifteen 

 days before. Two days after impregnation the flask B be- 



* The carbonaceous supply, as we remarked, had failed them, and to this 

 failure the absence of vital action, nutrition, and multiplication was at- 

 tributable. The liquid, however, contained butyrate of lime, a salt possess- 

 ing properties similar to those of the lactate. Why could not this Fait 

 equally well support the life of the vibrios? The explanation of the diffi- 

 culty seems to us to lie simply in the fact that lactic acid produces heat 

 by its decomposition, whilst butyric acid does not, and the vibrios seem 

 to require heat during the chemical process of their nutrition. 



8 To do this it is sufficient, first, to fill the curved ends of the stop- 

 cocked tubes of the flasks, as well as the India-rubber tube c c which 

 connects them, with boiling water that contains no air. 







