130 Microscopic Histochemistry 



3 ) Bennett's method. ^^— This method is based on the well- 

 known reaction between sulfhydryl groups and chloromer- 

 curiphenol. The reagent is p-chloromercuriphenylazo-^-naph- 

 thol, which is a poorly soluble red dyestuff. It will stain pro- 

 teins, containing -SH groups in a very specific way but in a 

 rather pale reddish shade. 



It would be interesting to synthesize chloromercuri-a- 

 naphthol, which should also combine with sulfhydryl groups. 

 In a second step, it could be coupled with a suitable diazo- 

 nium salt (e.g., Blue B Salt) to yield a very dark purple- 

 black azo dye. 



E. VARIOUS UNCLASSIFIED ORGANIC SUBSTANCES 



Flavoproteins 



Chevremont and Comhaire^ have devised a method for 

 the histochemical demonstration of riboflavin, based on the 

 fact that riboflavin, if first reduced to leucoflavin, will reoxi- 

 dize in air to red rhodoflavin. Since frozen sections of for- 

 malin-fixed material are used, only protein-bound riboflavin 

 will be demonstrated. 



Method 



Move frozen sections around in 1-2 per cent HCl, contain- 

 ing enough zinc dust to keep it bubbling, for about 30 min- 

 utes. Rinse sections in distilled water and expose them to air 

 for a few hours in a shallow layer of water. Mount in glyc- 

 erin-gelatin. Flavoproteins are stained red. 



This is an untested method. Sodium hydrosulfite 

 ( Na2S204 ) would be a simpler reducer than nascent hydro- 

 gen and just as effective. 



There is a possibility that flavoproteins could be localized 

 by their green fluorescence. The distinctive feature is the 



38. Bennett, H. S.: Anat. Rec., 100:640, 1948; Bennett, H. S., and 

 Yphantis, D. A.: J. Am. Chem. Soc, 70:3522, 1948; Mescon, H., and 

 Flesch, P.: J. Nat. Cancer Inst., 10:1370, 1950. 



1. Chevremont, M., and Comhaire, S.: Arch. f. exper. Zellforsch., 22:658, 

 1939. 



