854 LOUTS PASTEUR 



aspect from the dust of their cysts. This observation, we 

 may remark, furnishes one of the best proofs that can be 

 adduced against the spontaneous generation of vibrios or 

 bacteria, since it is probable that the same observation 

 applies to bacteria. It is true that we cannot say of mere 

 points of dust examined under the microscope, that one par- 

 ticular germ belongs to vibrio, another to bacterium ; but how 

 is it possible to doubt that the vibrios issue, as we see them, 

 from an ovum of some kind, a cyst, or germ, of determinate 

 character, when, after having placed some of those indeter- 

 minate motts of dust into clean water, we suddenly see, after 

 an interval of not more than one or two hours, an adult 

 vibrio crossing the field of the microscope, without our 

 having been able to detect any intermediate state between 

 its birth and adolescence? 



It is a question whether differences in the aspect and 

 nature of vibrios, which depend upon their more or less 

 advanced age, or are occasioned by the influence of certain 

 conditions on the medium in which they propagate, do not 

 bring about corresponding changes in the course of the 

 fermentation and the nature of its products. Judging at 

 least from the variations in the proportions of hydrogen 

 and carbonic acid gas produced in butyric fermentations, 

 we are inclined to think that this must be the case; nay, 

 more, we find that hydrogen is not even a constant product 

 in these fermentations. We have met with butyric fer- 

 mentations of lactate of lime which did not yield the 

 minutest trace of hydrogen, or anything besides carbonic 

 acid. FIG. 16 represents the vibrios which we observed in 

 a fermentation of this kind. They present 

 no special features. Butyl alcohol is, accord- 

 ing to our observations, an ordinary product, 

 although it varies and is by no means a 

 necessary concomitant of these fermenta- 

 tions. It might be supposed, since butylic 

 alcohol may be produced, and hydrogen be in 

 deficit, that the proportion of the former of 

 these products would attain its maximum 

 when the latter assumed a minimum. This, however, is by 

 no means the case; even in those few fermentations that we 





