THE INDIRECT ATTACHMENT OF DYES TO TISSUES 227 



negative, ^^^ presumably because the iodine is free to escape into 

 the alcohol. If 0-25% of iodine be added to the alcohol, the ex- 

 traction of the dye from Gram-negative bacteria is prevented and 

 they therefore appear to be Gram-positive.^^'^ 



If this first possibility is true, it follows that iodine does not 

 influence the affinity of the dye for the objects it colours, but only 

 prevents its subsequent escape. 



If the second possibility is true, the object/dye/iodine complex 

 may have special properties of its own ; that is, it may not only be 

 less easily split by ethanol than the object/dye compound, but may 

 also have special affinities, so that the objects coloured will not be 

 exactly the same as those coloured by the dye alone. This appears 

 to be the opinion of Panijel,^^- who has made a careful study of 

 crystal violet trapped by iodine. We have, however, no knowledge 

 of the chemical reactions involved, if indeed the triple complex is 

 actually formed. 



