152 



Biological Stains 



necessary to select between these two formulae the one best suited 

 to the particular batch of fuchsin to be employed. It is also well 

 recognized today that many basic fuchsins contain an impurity 

 which does not completely decolorize under the action of sulfite, 

 and which becomes evident in ^uch a reduced solution by the 

 yellowish, or even brownish pigment remaining. The nature of 

 this pigment has not been learned, altho Scanlan and Melin (1937) 

 report an investigation of the subject. Following the publication 

 of Scanlan and Melin's paper, the stain companies have begun to 

 find ways of preparing fuchsins that are free from the undesirable 

 impurity; and batches submitted for certification since then have 

 ordinarily proved satisfactory for the Feulgen technic as well as 

 for the other purposes discussed above. Not long after the above 

 paper appeared Coleman (1938) reported a method of eliminating 

 this impurity from a decolorized fuchsin by agitation with a de- 

 colorizing carbon; his method seems to make a sample of this dye 

 usable in the Feulgen technic, even though previously entirely un- 

 satisfactory. The histochemists, however, want a glass-clear 

 Schiff reagent; and modern producers of stains in America are 

 doing their best to supply basic fuchsins that will suit. This is at 

 present one of the tests applied to samples submitted for certifi- 

 cation. Lillie (1951) has contributed considerable information 

 on the subject. 



PROCEDURES RECOMMENDED BY THE COMMISSION IN WHICH THIS DYE IS USED 



