72 Microscopic Histochemistry 



entirely clear, but it is reasonably safe to asume that the im- 

 derlying chemical change is not the detachment or attach- 

 ment, respectively, of sulfuric groups to a polysaccharide. 

 It is much more likely that a maximum number of carboxylic 

 groups favors metachromasia; these are present in some sub- 

 stances (mucin, amyloid, etc.) and are destroyed by pro- 

 longed chromation. They are absent in other substances 

 (glycogen, starch, mucoid) but can be produced via the 

 intermediate stage of aldehydes by the same oxidative treat- 

 ment. In any case, overchromated glycogen appears to be an 

 example of a nonsulfate polysaccharide exhibiting true meta- 

 chromasia. The latest addition to the substances exhibiting 

 true metachromasia is ribose nucleic acid. This substance was 

 always considered to be nonmetachromatic ( in Lison s sense ) ; 

 however. Flax and Himes^^ have shown that under certain 

 conditions (specifications not clear) it will stain in a strongly 

 metachromatic shade, resistant to alcohol. 



Popper, Gyorgy, and Goldblatt^"^ described a peculiar 

 metachromasia of ceroid stained with methyl green (not 

 stated whether or not free from methyl violet). The nature 

 of this metachromasia has not been investigated; it may be 

 related to that of myelin as seen with the techniques of Feyr- 

 ter^^ and Chang. ^^ Wislocki and Singer ^^ believe that Feyr- 

 ter's metachromasia is due to the presence of sulfatides. 



Metachromasia of the mucinoid substances, heparin and 

 chondroitinsulfuric acid, on the one hand, and that of amy- 

 loid, on the other, are somewhat diflFerent, although, accord- 

 ing to recent investigations, amyloid (not included in Meyer's 

 classification) is a polysaccharide sulfate, closely similar to 



66. Flax, M. H., and Himes, M. H.: Anat. Rec, 108:529, 1950; Himes, 

 M. H., and Flax, M. H.: Anat. Rec, 108:539, 1950. 



67. Popper, H., Gyorgy, P., and Goldblatt, H.: Arch. Path., 37:161, 1944. 



68. Feyrter, F.: Virchows Arch. f. path. Anat., 296:645, 1936; Feyrter, F.: 

 Wien. Idin. Wchnschr., 55:461, 1942; Feyrter, F., and Pischinger, A.: Wien. 

 IcHn. Wchnschr., 55:463, 1942. 



69. Min-Chueh Chang: Anat. Rec, 65:437, 1938. 



70. Wislocki, G. B., and Singer, M.: J. Comp. Neurol., 92:71, 1950. 



