CHEMICAL CRITERIA OF ANAEROBIOSIS 



11 



test and those which reduce methylene blue in n/1000 NaOH. 

 These carbohydrates are also most susceptible to alkahne- 

 hydrolysis. The trisaccharid raffinose and the poly-saccharids 

 inulin and dextrin are generally considered not to give Fehhng's 

 test; they are less easily hydrolysed by alkahs, and they require 

 therefore a stronger concentration of alkali to reduce methylene 

 blue. The disaccharide, sucrose, and the alcohols, dulcitol and 

 mannitol, are especially resistant to alkalis: they respond there- 

 fore to neither Fehling's nor the methylene blue test. But 

 preliminary treatment of sucrose with n/100 HCl readily hydro- 

 lyses it and the overneutralization of such a mixture to n/100 

 alkalinity causes it to decolorize methylene blue quickly on 

 heating. 



Quantitative relations 



Tn many of the experiments up to this point the importance 

 of quantitative relations was recognized. 



We have just seen that a minute quantity of alkali (n/1000 

 NaOH) suffices to insure decolorization of certain carbohydrates 

 in 1 per cent solution with 0.00005 gram methylene blue per 

 cubic centimeter. The rapidity of decolorization of glucose 

 solution varies according to the concentration of alkah, which, 

 if sufficiently strong, effects the destruction of color without 

 heating: furthermore, less alkali is required to effect the loss of 

 color under anaerobic conditions than in the presence of the air. 

 The following is abstracted from a protocol covering an experi- 

 ment with 1 per cent glucose, 1 : 10,000 methylene blue, of vary- 

 ing degrees of alkalinity as indicated, placed in constricted tubes 

 with marble seals and read after twenty-four hours incubation 

 at 37°C. without preliminary heating. 



