Periodic acid–Schiff (PAS) is a staining method used to detect polysaccharides such as glycogen, and mucosubstances such as glycoproteins, glycolipids and mucins in tissues.
https://en.wikipedia.org/wiki/Periodic_acid–Schiff_stain

P.S. ШЙК = шифф-йодная кислота

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Note added at 34 мин (2019-07-20 10:57:43 GMT)
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Periodic acid-Schiff-alcian blue: a method for the differential staining of glycoproteins.

Abstract

The staining mechanism underlying the periodic acid-Schiff (PAS)-Alcian Blue (AB) sequence has been investigated using a variety of glycoprotein-containing tissues from different organs of the monkey, rat and mouse. The results obtained suggest that reactive carbohydrates contain at least three types of chemical end-groups found in neutral and acidic glycoproteins: (1) PA-engendered aldehyde groups coloured magenta by the Schiff reagent; (2) PA-engendered aldehyde groups coloured blue bisulphite-AB; and (3) naturally occurring acidic (carboxyl and/or sulphate) groups coloured blue by AB only. The PAS-AB sequence showed heterogeneity of glycoprotein structures in the conjunctiva and the duodenal goblet cells. Thus, the PAS-AB sequence is not the simple reverse sequence of AB-PAS but has its own definite and unique staining selectivity and can hence be used as a reliable method for the histochemistry of glycoproteins at the light microscope level.
https://www.ncbi.nlm.nih.gov/pubmed/2450077

Alcian Blue and PAS Staining Protocol

Principle

This is a combined method utilising the properties of both the PAS (see PAS) and Alcian blue (see Alcian blue) methods to demonstrate the full complement of tissue proteoglycans.

The rationale of the technique is that by first staining all the acidic mucins with Alcian blue, those remaining acidic mucins which are also PAS positive will be chemically blocked and will not react further during the technique. Those neutral mucins which are solely PAS positive will subsequently be demonstrated in a contrasting manner. Where mixtures occur, the resultant colour will depend upon the dominant moiety.
http://www.ihcworld.com/_protocols/special_stains/alcian_blu...

См. также: https://www.google.ru/search?newwindow=1&biw=1173&bih=825&ei...

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Note added at 37 мин (2019-07-20 11:00:10 GMT)
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ШИК-РЕАКЦИЯ (синоним: ПАС-реакция, реакция Шифф-йодная кислота) — гистохимический метод, применяемый для выявления углеводов, содержащих 1,2-гликолевые группы. С помощью ШИК-реакции в тканях человека и животных обнаруживают полисахариды, гликозаминогликаны, мукопротеины, гликопротеины, гликолипиды и фосфолипиды.
https://бмэ.орг/index.php/ШИК-РЕАКЦИЯ