ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



345 



will have separated in the shape of minute bubbles. This gas is got 

 rid of by shaking- the bulb like a clinical thermometer and heating the 

 tube gentlv near the free surface of the fluid. 



When the Ijulbs have been prepared in this way they can be kept 

 for several weeks ready for use. The fluid remains in position, provided 

 the tubes have been filled exactly as stated above. When the bulbs 

 have to be stored for several days l)efore being used, it is best to keep 

 them with the bulb down, the mouth remaining protected by the 

 supporting tube. 



The fermentation tubes are easily inoculated by means of a platinum 

 needle or loop brought in contact with the surface of the fluid, and 

 gently shaken in it. The needle may be removed carefully, so as not 



1. Burette containing one of the sterilized fermentable 

 media. The medium has been sterilized in the burette. 

 The capillary delivery pipe is protected by a glass sheath 

 until it is going to be used. 



2. Fermentation bulb (sterilized) ready to be filled 

 with the fermentable medium through the capillary de- 

 livery pipe of the burette. (A long hypodermic needle is 

 suitable for this purpose.) 



3. Fermentation bulb in a sterilized supporting glass 

 tube. Sets of these tubes containing series of ferment- 

 able media are kept ready for use in racks. 



i. Fermentaton tube taken out of its supporting tube 

 and inoculated by means of a platinum or palladium* 

 needle. A Pasteur's pipette of suitable shape can also 

 be used in the same way, but care , has to be exercised 

 to avoid an excess of fluid. 



5. Result of a test with production of gas and change 

 of reaction of the medium. 



* Owing to the difficulty of obtaining platinum at the 

 present time, I have adopted palladium as a substitute for 

 platinum, after ascertaining that this metal has no appre- 

 ciable lethal action on bacteria. 



to cause any of the fluid to be carried to the mouth of the tube. This 

 does not happen readily if the tubes are kept mouth upwards during 

 inoculation. 



All the reactions which can be observed in other kinds of apparatus 

 are ol)served clearly in my bulbs, which present important advantages 

 over the Durham's tubes at present in general use : — 



1. The total amount of gas generated under aerobic and partly 

 anaerobic conditions out of a certain amount of medium is collected. 



2. The first stages of the reaction are easy to observe, can l»e 

 detected very early, and can be easily timed. 



3. The colour of the litmus, when this indicator is used, is not 

 afl^ected by sterilization, as it is in the Durham's tubes. 



4. The amount of fluid used is very small. 



5. The fermentation bulb is not expensive. 



