16 IVAN C. HALL 



decolorized (yellow) in this condition by further boiling; further- 

 more, prolonged boiling of glucose, levulose, and lactose in strongly 

 acid solutions also results ultimately in more or less complete 

 decolorization of methylene blue. 



Some of the organic acids were noted above as failing to furnish 

 conditions necessarj^ for the decolorization of heated methylene 

 blue solutions even in the presence of glucose. Alone in n/10 

 concentration, neutralized with equivalent amounts of n/10 

 NaOH, and alkalinized to n/10 NaOH, they also fail. Neither 

 formaldehj^de, a building stone of glucose, nor ethyl alcohol, 

 one of the most frequent fermentation products of glucolysis, 

 in 5 per cent solution, acidified with HCl to n/10, neutral, or 

 alkaHnized to n/10 NaOH, causes the decolorization of meth- 

 ylene blue solutions containing 1 part per 100,000 on boiling. 

 Other products of alkali glucolysis must be tested if we are to 

 fasten the responsibility for the decolorization of methylene blue 

 upon a definite single substance. Our present speculations lead 

 us to suspect that decolorization of methylene blue depends upon 

 those conditions which liberate nascent hydrogen and, that the 

 formation of metallic glucosates by alkalis is somewhat analogous 

 in this respect to the action of HCl on zinc. Or, it may be that 

 the hydrogen required for the reduction of methylene blue to 

 its leuco-base is derived from the dissociation of water and corre- 

 sponds to the equivalent oxygen uniting with the residue of the 

 sugar molecule, according to Nef 's theory. 



Two per cent Witte's peptone solutions and 2 per cent agar 

 solutions with 1:100,000 methylene blue are decolorized by 

 heating with alkali. But with peptone, at least 1 part n/1 

 NaOH in 128 had to be present, owing possibly to the consider- 

 able buffer action of peptone. With agar solutions (pH = 7) 

 decolorization occured with 1 part N/1 NaOH per 200 agar but 

 not with 1 part per 250, although agar is supposed to have httle 

 or no buffer action according to Clark and Lubs (1917). x\ddi- 

 tion of 0.5 per cent glucose did not permit decolorization in less 

 alkah than in controls without glucose, in fact the presence of 

 agar inhibits decolorization in concentrations of alkaline glucose 

 solution which will readily decolorize without the agar. 



