Cultivation 



387 



vate because it will not grow where the smallest amount 

 of free oxygen is present. It is hence a typical obligatory 

 anaerobe. Farran * and Grixoni believe it to have originally 

 been an optional anaerobe, and it is said by these writers 

 that the organism can gradually be accustomed to oxygen 

 so as to grow in its presence. When this is achieved, it 

 loses its virulence. 



Fig. 1 1 8. Bacillus tetani; six- Fig. 119. Bacillus tetani; cul- 



days-old puncture culture in glu- ture four days old in glucose- 

 cose-gelatin(FrankelandPfeiffer). gelatin (Frankel and Pfeiffer). 



The methods for excluding the oxygen from the cul- 

 tures and replacing it by hydrogen, as well as other methods 

 suggested for the cultivation of the strictly anaerobic 

 organisms, are given under the appropriate heading (Anae- 

 robic Cultures), and need not be repeated here. 



* "Centralbl. f. Bakt. u. Parasitenk.," July 15, 1898, p. 28. 



