62 Microscopic Histochemistry 



ly granular distribution, resembling that seen in frozen-dried 

 preparations.^- The temperature of fixation seems to be of 

 considerable importance. Liver contains a powerful glyco- 

 genolytic enzyme system, which, unless the tissue is chilled 

 promptly, may cause a considerable loss of glycogen, espe- 

 cially in the interior of thick blocks. This loss may be quite 

 conspicuous in sections stained with Bauer's^^ or Best's^* 

 methods, while it may not be noticeable at all if the Hotch- 

 kiss-McManus"^' ^^ technique is used— an indication of a 

 change in the constitution of the molecule rather than of 

 actual disappearance. Although the glycogen found in other 

 tissues is much more stable, it is, safer to perform fixation 

 of all tissues in the refrigerator. 



Frozen sections, as a rule, cannot be used for the staining 

 of glycogen. Celloidin- or parafiin-embedding are equally 

 good. 



A) Methods specific for the group in general— These 

 methods are based on aldehyde reactions after oxidative 

 pretreatment. 



Choice of the oxidizing agent —The two oxidizers most 

 often employed are chromic acid and periodic acid. Chromic 

 acid is the agent of choice if a selective staining of glycogen 

 and/or mucin is desired. Besides these two substances, 

 starch, galactogen, cellulose, tunicin, chitin, and colloid of 

 the thyroid follicles will also react more or less strongly after 

 chromic acid oxidation. Glycoproteins of the connective tis- 

 sue remain almost completely unstained, and for this reason 

 the contrast between glycogen and /or mucin and the back- 

 ground is quite sharp. It is a curious fact that Bauer^^ in his 

 original paper on the chromic acid-Schi£F method explicitly 

 states that mucin does not stain; all subsequent workers have 

 found that it stains quite intensely. After periodate oxidation, 

 all the substances previously mentioned will react, and, in 



33. Bauer, H.: Ztschr. f. mikr.-anat. Forsch., 33:143, 1933. 



34. Best, F.: Ztschr. f. wissensch. Mikr., 23:319, 1906. 



35. McManus, J. F. A.: Nature, 158:202, 1946. 



