Chapter J_9 



Feulgen and PAS 



Technics, and 



Related Reactions 



Feulgen and PAS technics involve two chemical reactions: (1) the 

 oxidation of 1,2 glycols and/or a-amino alcohol groups to aldehydes, 

 and (2) the reaction of resulting aldehydes with Schiff reagent (page 

 294) to form a purple-red color. Among the polysaccharides are gly- 

 cogen, starch, and cellulose having 1,2 glycol groups which develop a 

 positive Schiff reaction. Cartilage has a polysaccharide compound mak- 

 ing this tissue react positively; and among the mucoproteins, the 

 mucins are carbohydrates and thus react positively. Other structures of 

 unknown chemical composition, but containing polysaccharides, will 

 show a positive reaction: striated and brush borders and reticulin 

 fibers, for example. The two oxidizers most commonly used are chromic 

 and periodic acids. The latter breaks the carbon chains of the poly- 

 saccharides containing the 1,2 glycol groupings and oxidizes the broken 

 ends into aldehyde gToups. Chromic acid is a weaker oxidizer with its 

 action limited almost exclusively to glycogen and mucin (the principle 

 of the Bauer method, page 301). If necessary, glycogen and starch can 

 be demonstrated to the exclusion of other reactants, by iodine or Best's 

 Carmine (page 267), and mucin by Mayor's mucicarmine (page 273) or 

 metachromatic methods (page 278). If it is desirable to prevent the 

 reaction of glycogen or starch, the saliva or diastase treatment is simple 

 and effective. 



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