120 Microscopic Histochemistry 



D. PROSTHETIC GROUPS 

 Phenolic Substances, Especially Polyphenols 



The list of phenolic substances foiuid in animal tissues in- 

 cludes tyrosine, adrenalin, certain propigments,^ the entero- 

 chromaffin substance, the phenolic ketosteroids, and a few 

 unidentified substances in lower species (oysters, cephalo- 

 pods,^ toads,^ etc.^). Tyrosine was dealt with in the section 

 on amino acids (p. 113). Phenolic ketosteroids have never 

 been investigated histochemically except in a very uncritical 

 way by Seeger.^ This section will be devoted especially to 

 adrenalin and the enterochromaflBn substance. Before going 

 into the specific histochemical properties of these substances, 

 a few words must be said about color reactions for phenols. 



There are a number of characteristic color reactions for 

 phenols, some of which can be utilized for their histochemical 

 identification. They will be enumerated in the order of their 

 importance. 



1) The azo-coupling reaction.— At an alkaline reaction, 

 phenols will couple with diazonium salts to form intensely 

 colored, water-insoluble azo dyes.^ The shade of the dye de- 

 pends on both the phenolic and the diazoic components; as a 

 rule, a relatively low molecular weight of the components 

 expresses itself in yellowish or orange shades; with increas- 

 ing complexity of the molecule the shade will shift from 

 orange to red, to purple, and finally to blue and black. How- 

 ever, besides molecular weight, structure is also an important 

 determinant of shade; azo dyes produced from a- and /3- 



1. Lison, L.: Compt. rend. Soc. de biol., 106:41, 1931. 



2. Lison, L.: Histochimie animale, pp. 158-59 (Paris, 1936). 



3. Shipley, P. G., and Wislocki, G. B.: Contrib. Embryol., 3:73, 1915; 

 Lison, L.: Compt. rend. Soc. de biol., 111:657, 1932. 



4. Lison, L.: Compt. rend. Soc. de biol., 112:1237, 1933. 



5. Seeger, P. G.: Ztschr. f. mikr.-anat. Forsch., 46:153, 1939. 



6. Saunders, K. H.: The aromatic diazo-compomids and their technical 

 applications (London: Edward Arnold & Co., 1936); Pratt, L. S.: The 

 chemistry and physics of organic pigments (New York: John Wiley & Sons, 

 1947). 



