304 STUDIES OX FERMENTATION. 



not doubtful. To assure ourselves further of the effect of air on 

 the vibrios, we half filled two test tubes with the fermenting 

 liquid taken from another fermentation which had also attained 

 its maximum of intensity, into one of which we passed a 

 current of air, into the other carbonic acid gas. In the course 

 of half an hour, all the vibrios in the aerated tube were dead, or 

 at least motionless, and fermentation had ceased. In the other 

 tube, after three hours* exposure to the effects of the carbonic 

 acid gas, the vibrios were still very active, and fermentation 

 was going on. 



There is a most simple method of observing the deadly effect 

 of atmospheric air upon vibrios. We have seen in the micro- 

 scopical examination made by means of the apparatus repre- 

 sented in Fig. 71, how remarkable were the movements of the 

 vibrios when absolutely deprived of air, and how easy it was to 

 discern them. "VVe will repeat this observation, and at the 

 same time make a comparative study of the same liquid, under 

 the microscope, in the ordinary way, that is to say, by placing 

 a drop of the liquid on an object-glass, and covering it with a 

 thin glass slip, a method which must necessarily bring the drop 

 into contact with air, if only for a moment. It is surprising 

 what a remarkable difference is observed immediately between 

 the movements of the vibrios in the bulb and of those under 

 the glass. In the case of the latter we generally see all 

 movement at once cease near the edges of the glass, where the 

 drop of liquid is in direct contact with the air ; the movements 

 continue for a longer or shorter time about the centre, in pro- 

 portion as the air is more or less intercepted by the vibrios at 

 the circumference of the liquid. It does not require much skill 

 in experiments of this kind to enable one to see plainly that 

 immediately after the glass has been placed on the drop, which 

 has been affected all over by atmospheric air, the whole of the 

 vibrios seem to languish and to manifest symptoms of illness — 

 we can think of no better expression to explain what we see 

 taking place — and that they gradually recover their activity 

 about the centre, in proportion as they find themselves in a 



