Formazan Reaction as a Confirmatory Test for Aldehyde Groups in Histochemistry

Abstract

ONE of us has predicted elsewhere¹ that not all neutral mucopolysaccharides can be demonstrated in tissue sections by the periodic acid–Schiff technique because the ‘dialdehydes’ which are formed by the periodate oxidation of their vic-glycol groups may be transformed into hemiacetals or hemialdals which are known to be unreactive towards Schiff's reagent in vitro². On the other hand, all periodate-engendered ‘dialdehydes’ appear to react with aromatic hydrazines^2,3 including salicyloyl hydrazide and 2-hydroxy-3-naphthoic acid hydrazide¹. Therefore, in tissues which have been treated with periodic acid, those mucin sites which take up hydrazine reagents but not Schiff's solution probably contain ‘dialdehydes’ in the hemialdal and/or hemiacetal forms. This hypothesis has now been confirmed by showing that the formazan reaction is negative in these sites.