344 LOUIS PASTEUR 



hypothesis of an original relation between the two produc- 

 tions, butyric fermentation ought in every case to follow 

 the growth of bacteria. 



We may also call attention to another striking experiment, 

 well suited to show the effect of differences in the composi- 

 tion of the medium upon the propagation of microscopic 

 beings. The fermentation which we last described com- 

 menced on March 27th and continued until May loth; that to 

 which we are now to refer, however, was completed in four 

 days, the liquid employed being similar in composition and 

 quantity to that employed in the former experiment. On 

 April 23, 1875, we filled a flask of the same shape as that rep- 

 resented in FIG. n, and of similar capacity, viz., 6 litres, 

 with a liquid composed as described at page 69. This liquid 

 had been previously left to itself for five days in large 

 open flasks, in consequence of which it had developed an 

 abundant growth of bacteria. On the fifth day a few bubbles, 

 rising from the bottom of the vessels, at long intervals, be- 

 tokened the commencement of butyric fermentation, a fact, 

 moreover, confirmed by the microscope, in the appearance of 

 the vibrios of this fermentation in specimens of the liquid 

 taken from the bottom of the vessels, the middle of its mass, 

 and even in the layer on the surface that was swarming 

 with bacteria. We transferred the liquid so prepared to the 

 6-litre flask arranged over the mercury. By evening a 

 tolerably active fermentation had begun to manifest itself. 

 On the 24th this fermentation was proceeding with aston- 

 ishing rapidity, which continued during the 25th and 26th. 

 During the evening of the 26th it slackened, and on the 27th 

 all signs of fermentation had ceased. This was not, as might 

 be supposed, a sudden stoppage due to some unknown cause ; 

 the fermentation was actually completed, for when we ex- 

 amined the fermented liquid on the 28th we could not find 

 the smallest quantity of lactate of lime. If the needs of in- 

 dustry should ever require the production of large quantities 

 of butyric acid, there would, beyond doubt, be found in the 

 preceding fact valuable information in devising an easy 

 method of preparing that product in abundance. 4 



* In what way are we to account for so great a difference between the 

 two fermentations that we have just described? Probably it was owing to 

 some modification effected in the medium by the previous life of the bac- 



1 



