186 



BACTERIOLOGY. 



FIG. 35. 



this group a number of devices are employed for the 

 exclusion of oxygen from the cultures. 



Koch's method. Koch covered the surface of a gel- 

 atin plate, which had been previously inoculated, with a 

 thin sheet of sterilized isinglass. The organisms which 

 grew beneath it were supposed to grow without oxygen. 

 Hesse's method. Hesse poured sterilized oil upon the 

 surface of a culture made by stabbing into a tube of 

 gelatin. The growth that occurred along the track of 

 the needle was supposed to be anaerobic in nature. 



Methods of Liborius. Liborius has suggested two 

 useful methods for this purpose. The one is to fill a 

 test-tube about three-quarters 

 full of gelatin or agar-agar, 

 which, after having been ster- 

 ilized, is to be kept in a vessel 

 of boiling water for ten min- 

 utes to expel all air from it. 

 It is then rapidly cooled in 

 ice-water, and when between 

 30 and 40 C., still fluid, is 

 to be inoculated and very rap- 

 idly solidified. It is then 

 sealed up in the flame. An- 

 aerobic bacteria develop only 

 in the lower layers of the 

 medium. His other method is 

 that in which he employs a 

 special tube, known as "the 

 Liborius tube." Its construc- 

 tion is shown in Fig. 35. 



Liborius's tube for anaerobic 

 cultures. 



Through the side tube hydrogen is passed until all air 

 is expelled ; the contracted parts, both of the neck of the 



