308 STUDIES ON FEKMENTATION. 



medium in which they propagate, do not bring about corre- 

 sponding 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. ^Ve have met with 

 butyric fermentations of lactate of lime which did not yield 

 the minutest trace of hj'drogen, or anything besides carbonic 

 acid. Fig. 74 represents the vibrios which we observed in a 



Fig. 74. 



fermentation of this kind. They present no special features. 

 Butj'l alcohol is, according to our observations, an ordinary 

 product, although it varies and is by no means a necessary con- 

 comitant of these fermentations. 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, how- 

 ever, is by no means the case ; even in those few fermentations 

 tliat we have met with in which hydrogen was absent, there 

 was no formation of butylic alcohol. 



From a consideration of all the facts detailed in this para- 

 graph we can have no hesitation in concluding that, on the 

 one hand, in cases of butyric fermentation, the vibrios which 

 abound in them and constitute their ferment, live without air 

 or free oxygen ; and that, on the other hand, the presence of 

 gaseous oxygen operates prejudicially against the movements 

 and activity of those vibrios. But now does it follow that the 



