CULTURE MEDIA WITH WIDE RANGE OF HYDROGEN 



327 



in 2 per cent agar it will be seen that 20 times this volume of acid 

 and 9 times this volume of alkali were employed. Manifestly 

 these limits are only approximate and could be more accurately 

 determined by improved technic. They are, however, far beyond 

 the Imiits of tolerance of microorganisms and are intended only to 

 show that hydrogen or hydroxyl ion concentration need not be 

 limiting factors in the preparation of solid agar media. 



TABLE 1 



Effect of atid and alkali on solidification of agar 



All of the agar media in these series appear to be able to remain 

 solid for an indefinite period when they are maintained at room 

 temperature. If, however, they are autoclaved and then cooled 

 all of the acid media were found to remain liquid, whereas the 

 tubes of 1 per cent agar with 0.1 cc. NaOH and 2 per cent agar 

 with 0.1 and 0.2 cc. NaOH became solid again. 



Considerably larger amounts of acid or alkali must be added 

 to 10 and 15 per cent gelatin to destroy the jellifying power as 

 shown in table 2. 



In the case of 10 per cent gelatin the limits are seen to be 

 about 9.02 per cent HCl and between 3.33 and 4 per cent NaOH, 

 and of 15 per cent gelatin between 9.02 and 10.15 per cent HCl 



JOURNAL OF BACTERIOLOGY, VOL. VI, NO. 3 



