296 STTDIES ON FEKMENTATIOX. 



completely fill a flask willi the liquid, and place it in the oven, 

 merely avoiding any addition of butyric vibrios before the 

 lapse of two or three days. "VVe may wait even longer ; and 

 then, if the liquid does not become impregnated spontaneously 

 with vibrio germs, the liquid, which at first was turbid from 

 the presence of bacteria, will become bright again, since the 

 bacteria when deprived of life, or, at least, of the power of 

 ntoving, after they have exhausted all the oxygen in solution, 

 will fall inert to the bottom of the vessel. On several occasions, 

 we have determined this interesting fact, which tends to prove 

 that the butyric vibrios cannot be regarded as another form of 

 bacteria, inasmuch as, on the hypothesis of an original relation 

 between the two productions, butyric fermentation ought in 

 every case to follow the growth of bacteria. 



"VVe may also call attention to another striking experiment, 

 well suited, to show the effect of differences in the composition 

 of the medium upon the propagation of microscopic beings. 

 The fermentation which we last described commenced on 

 March 27th and continued until May 10th ; 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 23rd, 

 1875, we filled a flask of the same shape as that represented 

 in Fig. 69, and of similar capacity, viz., 6 litres, with a liquid 

 composed as described at page 293. 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, betokened the com- 

 mencement 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 trans- 

 ferred the liquid so prepared to the 6-litre flask arranged over 

 the mercury. By evening a tolerably active fermentation had 



