548 REUBEN L. KAHN 



formaldehyd added to the Endo medium produces a purple- 

 violet color. 



The underlying cause of the different views expressed by these 

 investigators, appears to be due to the variation in the strength 

 of the reagents employed in their respective experiments. It 

 has been observed again and again that fuchsin decolorized with 

 sodium sulfite will behave differently toward different dilutions 

 of the same reagent. The behavior of the fuchsin sodium sulfite 

 solution toward strong and weak acid, or strong and weak 

 aldehyd is such that it can not be compared. Furthermore, 

 the quantity of sodium sulfite employed in the decolorization 

 of the fuchsin also appears to play an important part in such 

 experiments. 



The fuchsin-sulfite combination is extremely unstable. Work- 

 ers have long learned not to expect complete decolorization of 

 the fuchsin with sodium sulfite in hot solutions, because of the 

 dissociation under these conditions. When an Endo plate is 

 exposed to air, the color of the medium becomes pink, probably 

 because the sulfite in the presence of air is oxidized to sulfate, 

 causing the fuchsin color to reappear in part. Very dilute 

 acids also bring out the color to some extent, possibly because 

 of the high degree of dissociation that exists in the mixture. 



If inorganic acids of moderate strength be added to fuchsin 

 decolorized with sodium sulfite, decolorization becomes even 

 more complete. The sodium probably combines with the acid 

 to form a salt, liberating sulfur dioxide or sulfurous acid, and 

 causing further decolorization. Concentrated acids will reduce 

 the color of basic fuchsin without the presence of sodium sulfite. 



Organic acid added to decolorized fuchsin will cause a reap- 

 pearance of the color, due possibly to a stronger affinity of basic 

 fuchsin for the organic acid than for the inorganic sulfite, the 

 result being the formation of acid fuchsin. 



It might be said in this connection that we are dealing here 

 with an extremely complex organic combination, and it is ques^ 

 tionable to what extent one is permitted to draw a conclusion 

 from a simple test tube experiment. The following few obser- 

 vations will be recorded with the hope that they may throw 



