STUDIES ON FERMENTATION. 305 



part of the medium fhat is less aflfected by the presence of 

 oxygen. 



Some most curious facts are to be found in connection with 

 an observation, the correhitive 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 cessation of motion in all the 

 bacteria which lie in the central portion of the liquid, where the 

 0x3' gen rapidly disappears to supply the necessities of the bacteria 

 existing there ; whilst, on the other hand, near the edges of the 

 cover-glass the movements are very active, in consequence of 

 the constant supply of air. In spite of the speedy death of the 

 bacteria beneath the centre of the glass, we see life prolonged 

 there if by chance a bubble of air has been enclosed. All 

 round this bubble a vast number of bacteria collect in a thick, 

 moving circle, but as soon as all the ox3^gen of the bubble has 

 been absorbed they fall apparently lifeless, and are scattered by 

 the movement of the liquid.* 



We vaay here be permitted to add, as a purely historical 

 matter, that it was these two observations just described, made 

 successively one day in 1861, on vibrios and bacteria, that first 

 suggested to us the idea of the possibility of life without air, 

 and caused us to think that the vibrios which we met so fre- 

 quently in our lactic fermentations must be the true butyric 

 ferment. 



We may pause a moment to consider an interesting question 

 in reference to the two characters under which vibrios appear 

 in butyric fermentations. What is the reason that some vibrios 

 exhibit refractive corpuscles, generally of a lenticular form, 



* We find this fact, which we published as long ago as 1863, confirmed 

 in a work of H. Hoffmann's published in 1869, under the title Memoire 

 sur lea baderies, which has appeai'ed in French [Annales cles Sciences 

 naturelles, 5th series, vol. xi.). On this subject we may cite an observa- 

 tion that has not yet been published. Aerobian bacteria lose all power of 

 movement when suddenly plunged into carbonic acid gas ; they recover 

 it, however, as if they had only been suffering from anaesthesia, as soon 

 as they are brought into the air again. 



X 



