FERMENTATION TUBES 83 



the oil or mercury. When the air has been entirely 

 displaced the glass tube is removed, the bell- jar weighted, 

 and the whole placed in the incubator. Bulloch's apparatus 

 is somewhat similar to this. Wide- mouthed jars with 

 well -ground glass lids, which are luted down, are very 

 convenient, the oxygen being absorbed with alkaline 

 pyrogallol placed at the bottom, and the Petri dishes 

 stacked on a glass capsule or other support to raise them 

 above the fluid. 



The Esmarch roll cultures can be adapted for anaerobic 

 cultures. The wool plug is replaced by a rubber cork 

 with two holes, through which inlet and outlet glass 

 tubes pass, as in Frankel's anaerobic tubes (Fig. 12). The 

 gelatin (or agar) having been melted and inoculated, the 

 medium is kept melted in a water- bath at appropriate 

 temperature, the hydrogen is passed through for a quarter 

 of an hour, the tubes are sealed oft', and the roll- culture is 

 prepared. 



Golding's flask (p. 79) or a " plate " bottle (Fig. 15) 

 may be similarly used, or a Golding flask may be inverted 

 over a beaker of alkaline pyrogallol. 



For the detection of fermentation and gas production, 

 stab cultures in glucose agar or shake cultures in gelatin 

 may be employed. For the latter a tube of gelatin 1 is 

 melted at a low temperature, inoculated with the organism, 

 and allowed to solidify in the upright position ; the 

 organism is thereby distributed throughout the medium. 

 Fermentation with gas production is indicated by the 

 presence of gas bubbles, or even by the disruption of the 

 medium. Durham's fermentation tubes are very con- 

 venient for showing fermentation. These are test-tubes 

 containing suitable fluid media (10 c.c. each) into which 

 small glass tubes closed at the upper end are placed ; the 



1 Lemco gelatin frequently gives no gas ; a meat-broth gelatin 

 should therefore be used for gelatin shake cultures. 



