346 



LOUIS PASTEUR 



microscopical examination of these vibrios, quite out of 

 contact with' air, is the following. After butyric fermenta- 

 tion has been going on for several days in a flask, (Fie. 13), 

 we connect this flask by an india-rubber tube with one of 

 the flattened bulbs previously described, which we then 

 place on the stage of the microscope (FiG. 13). When we 



V 



Fie. 13 



wish to make an observation we close, under the mercury, 

 at the point b, the end of the drawn-out and bent delivery- 

 tube. The continued evolution of gas soon exerts such a 

 pressure within the flask, that when we open the tap r, 

 the liquid is driven into the bulb II, until it becomes quite 

 full and the liquid flows over into the glass V. In this 

 manner we may bring the vibrios under observation with- 

 out their coming into contact with the least trace of air, 

 and with as much success as if the bulb, which takes the 

 place of an object glass, had been plunged into the very 



