CHEMICAL CRITERIA OF ANAEROBIOSIS 



CeHs— N(CH3)2 



> 



C6H3-N(CH3)2C1 



N<^ >S 



which is reduced (Bernthsen 1885) by the action of zinc or zinc 

 chloride with HCl or H2SO4 and^in alkahne solution with am- 

 monium sulfate to leuco-methylene blue 



CsHs— N(CH3)2 



CeHa— N(CH3)2 



These formulae are generally accepted now, practically the only 

 disagreement being as to the duect bond between two of the 

 nitrogen atoms. 



Landauer and Weil (1910) also obtained leuco-methylene blue 

 by treating a solution of the blue salt in alcohol, with phenyl- 

 hydrazine, warming and cooling under CO2. It has a melting 

 point of 185°C. and is not oxidized even by pure oxygen in an 

 atmosphere free from acid and in strongly alkaline solutions is 

 not acted upon by permanganate or hydrogen peroxide. The 

 following equation represents the reaction 



C6H3— N(CH3)2 

 n/ \s +NH2NHC6H5 = 



CeHa— N(CH3)2C1 

 (blue) 

 C6H3— N(CH3)2 

 Hn/ \s + CbHg + N2 + HCl 



CeHs— N(CH3)2 



(colorless) 



Excepting Landauer and Weil (1910) chemists have studied 

 methylene blue largely from the standpoint of action of inorganic 

 compounds upon it. We turn now to- a consideration of its 

 behavior in the presence of those factors which enter into bacteri- 

 ological culture media, since the custom, not altogether defensible, 



