The periodic acid-Schiff stain for the demonstration of fungi in animal tissue.

The routine histopathologic stains used for the demonstration of fungi in animal tissue are inadequate. The fungi are differentiated poorly and sometimes not at all. This is a limitation in the diagnosis of the mycotic granulomas in which the organisms may be rare. A definitive fungus stain, therefore, is needed, particularly by the pathologist and mycologist. During an attempt to stain the capsules of certain fungi, brilliant staining with the periodic-acid-Schiff-reagent technique (Hotchkiss-McManus stain) was observed. A survey of many different types of mycotic tissue revealed the general usefulness of this reaction in mycologic histopathology. The present communication presents the method and briefly reviews the pertinent literature. The chemistry of this and related reactions has been recently reviewed by DeLamater, Mescon, and Barger (1950). The various applications of the Schiff reagent have in common the requirement that the tissues must be hydrolyzed in such a manner as to release substances (usually aldehydes) that will recolorize and react with the Schiff reagent. The best known use of the Schiff reagent is in the Feulgen reaction, which is presujmably specific for aldehydes released from desoxyribonucleic acid by acid hydrolysis of the tissue. Under optimal conditions the nuclei only stain. The Bauer stain calls for prolonged hydrolysis of tissue in chromic acid (Lillie, 1947a). Under these conditions glycogen stains intensely red with the Schiff reagent. The Bauer reaction is an empirical procedure (Hotchkiss, 1948). Potassium permanganate or other oxidizing agents can be substituted for the chromic acid in the hydrolyzing process. How this may affect the chemical specificity of the reaction is not yet clear. It is not possible to predict from the chemical structure which substances will recolorize with the Schiff reagent. The chemistry of the periodic-acid-Schiff technique is fairly well understood (Hotchkiss). The substances stained by this procedure belong to the general class of carbohydrates. These must contain the 1,2-glycol grouping in unsubstituted form or the equivalent structure in which OH groups are replaced by amino or alkylamino groups. Jeanloz (1950), however, has stated that he believes structure has no definite relation to a positive reaction. Periodic acid