It has been shown that certain mucinous substances which are weakly positive with the periodic acid/Schiff technique stain more strongly after treating them with a solution of sodium hydroxide.

The deepening of the staining reaction is produced by making available, for aldehyde production by periodic acid, more .CHOH.CHOH., .CHOH.CHNH2., or .CHOH .CHNHR. groups. This is done without affecting those sulphate or metaphosphate groups responsible for metachromasia.

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