36 IVAN C. HALL 



The literature is notably deficient in accurate data on the 

 oxygen tension limits of anaerobic bacteria determined by vacu- 

 umetric methods. The limit of 35 cm. Hg pressure for the 

 vibrion septique set by Rosenthal (1906) in liquid media is of 

 doubtful value when viewed in the light of the recent obser- 

 vations of Harris (1919) on the apparently high tolerance of 

 B. sporogenes for oxygen in liquid cultures as compared with 

 agar slopes. 



WTiile we have tested the effect of inert gases in the case of 

 hydrogen and carbon dioxide, it is scarcely fair to consider the 

 results as necessarily corresponding to those obtained by cultural 

 methods where we conceive the action to be primarily physical, 

 since with methylene blue solutions we may also have chemical 

 reactions. Hydrogen, indeed, did decolorize cold solutions of 

 0.5 per cent glucose with n/500 NaOH and 1 : 100,000 methylene 

 blue slowly, and hot solutions already decolorized remained so 

 during fifteen minutes of active ebullition by hydrogen from a 

 Kipp generator loaded with zinc and sulfuric acid and purified 

 by passage through 10 per cent PhNOs and alkaline pyrogallol. 

 Furthermore when sealed the hot solution remained decolorized 

 till opened on the fourth day while the cold solution showed only 

 a trace of color while sealed. 



Passage of commercial carbon dioxide through similar solutions 

 of the dye for one hour failed to decolorize the cold solution 

 although the hot solution remained decolorized during this part 

 of the experiment but soon regained the blue color after sealing. 

 Reheating these solutions failed to decolorize either of them, 

 without further addition of alkali. Here is a situation, which, 

 barring the known inhibitive action due to improper acidity 

 for certain organisms, might yield satisfactory results in the 

 case of certain others, as Pasteur found, without permitting a 

 satisfactory degree of alkahnity for the decolorization of meth- 

 ylene blue. 



Coming now to the matter of chemical reduction of oxygen 

 tension, we conceive that in so far as regards reducing agents 

 in the medium, they have been sufficiently dealt with already, 

 and the necessity of recognizing limitations of time and space 



