CHAPTER IX. 

 THE CULTIVATION OF ANAEROBIC BACTERIA. 



The cultivation of micro-organisms which will not 

 grow where the least amount of oxygen is present is 

 always attended with much difficulty, and can seldom be 

 accomplished with certainty. Many methods have been 

 suggested, but not one can be described as satisfactory. 



Koch originally cultivated anaerobic bacteria upon 

 plates by covering the surface of the soft gelatin with a 

 thin film of mica previously sterilized by incandescence. 

 Some anaerobic forms will grow quite well by such a 

 simple exclusion of the air, but the strictly anaerobic 

 forms will not develop at all. 



Hesse originated the plan, still sometimes followed, of 

 making a deep puncture in recently boiled and rapidly 

 sterilized gelatin or agar-agar, then covering the surface 

 with sterilized oil, through which no oxygen was sup- 

 posed to penetrate (Fig. 35). 



The fermentation-tube devised by Smith is an excel- 

 lent ready means of determining that bacteria will de- 

 velop under anaerobic conditions. The obligatory aerobs 

 grow only in the bulb, the obligatory anaerobs only in 

 the closed tube, the facultative or optional organisms in 

 both. 



In order that the anaerobs can grow, Smith points out 

 that it is essential that the bouillon contains some sugar. 



Iyiborius suggested the plan of having a tube nearly 

 full of gelatin or agar-agar, boiling it just before inocu- 

 lation, so as to expand and drive out whatever air it 

 might contain, making the inoculation while the culture- 

 medium was still fluid, cooling rapidly in ice-water, and 

 sealing up the tube in a blowpipe as near the surface of 

 the gelatin as possible. 



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