42 Biological Stains 



dyes have greater affinity for nuclear substance, acid dyes for 

 cytoplasm is enough to suggest this possibility to anyone; but for 

 a long time the matter remained in the realms of theory, without 

 much concrete fact on which methods could be based. 



Undoubtedly the first real stimulus to histochemical technic 

 came from Feulgen and Grossenbeck's application of the Schiff's 

 reagent for aldehyde to cytological structures. (See p. 150). 

 Feulgen was not unaware of what he had accomplished, as shown 

 by the fact that he named the granules thus stained "nucleal" the 

 terminal syllable indicating their supposedly aldehyde-like nature. 

 That was about as far as one could go in those days; not until the 

 various nucleic acids came to be recognized and localized in the 

 cell could the specificity of the Feulgen reaction or the nature of 

 the bodies stained by it be learned. 



It was probably ten years or more after Feulgen's work before 

 the reaction named after him became well enough established so 

 that the Stain Commission regarded as a sufficiently important 

 use for basic fuchsin to serve as one of the criteria of certification. 

 It was realized that not all basic fuchsins were suitable for use in 

 the technic; and for some time it seemed an unnecessary refine- 

 ment to insist that a certified fuchsin should meet this requirement 

 when the dye was so seldom used for the purpose. Now, however, 

 the situation has changed greatly, thanks to the rapid development 

 of histochemical technic, and no basic fuchsin unsatisfactorv in the 

 Feulgen procedure would be acceptable. 



At present the efforts of histochemists are being directed toward 

 finding other reagents that are specific for the same or other cyto- 

 chemical features. Some of the reagents are dyes, others are not 

 dyes but develop color in the presence of the chemicals with which 

 they react. The proposal has been made to extend the principle 

 of stain certification to cover some of these reagents. No definite 

 plans to that effect have yet been made, but the project is being 

 given careful consideration at the present time. 



