THEORY OF FERMENTATION SSI 



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 microscopical examination made by means of the appa- 

 ratus represented in FIG. 13, how remarkable were the move- 

 ments of the vibrios when absolutely deprived of air, and 

 how easy it was to discern them. We will repeat this obser- 

 vation, 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 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 proportion as 

 the air is more or less intercepted by the vibrios at the cir- 

 cumference 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 part of the medium that is less affected 

 by the presence of oxygen. 



Some of the most curious facts are to be found in con- 

 nection with an observation, the correlative and inverse of 

 the foregoing, on the ordinary aerobian bacteria. If we 

 examine below the microscope a drop of liquid full of these 

 organisms under a coverslip, we very soon observe a cessa- 

 tion of motion in all the bacteria which lie in the central 

 portion of the liquid, where the oxygen rapidly disappears 

 to supply the necessities of the bacteria existing there; 

 whilst, on the other hand, near the edges of .the cover-glass 



