74 MICROSCOPIC TECHNIQUES 



poor. The Ehrlich reaction employing p-dimethylaminobenzal- 

 dehyde will give a violet color with phenols, aryl amines, and 

 heterocyclic compounds. Diazotization may indicate the same classes 

 of substances. The indophenin reaction utilizing isatin and sulfuric 

 acid gives a reddish-violet color in the presence of five-membered 

 heterocyclic compounds including indole. The nitrosamino reaction 

 of Lison converts the imino group in pyrrole or indole to a nitros- 

 amine by means of nitrous acid, and the nitrosamine is then made 

 to produce a green color through the Liebermann reagent (5% 

 phenol and concentrated sulfuric acid). This test is given by imino 

 groups, phenols, and primary aryl amines. The nitro reaction 

 enables differentiation between pyrroles and indoles; the sections 

 are treated with a mixture of equal parts of sulfuric and nitric acids, 

 and benzene ring compounds including indoles develop a canary 

 yellow color while pyrroles are not colored. 



PHENOLS 



Four main staining reactions have been employed for the detection 

 of phenols in tissue preparations. The azo reaction is based on diaz- 

 otization to form colored compounds; the indo reaction depends 

 on the formation of a green or blue indamine when an aromatic 

 para diamine is oxidized in the presence of tissue phenol; the 

 "argentaffin" reaction makes use of the reduction of ammoniacal 

 silver hydroxide and applies to ortho and para polyphenols, poly- 

 amines, and aminophenols ; and the "chromaffin" reaction, which is 

 used particularly to indicate adrenaline, gives rise to a brown color 

 when tissue is fixed with dichromate salts. A discussion of these tests 

 was given by Lison ( 1936, page 139-160) . The argentaffin test is 

 quite unspecific since many reducing substances can likewise give 

 a positive reaction. The chromaffin test is not entirely specific for 

 adrenaline, but has proved useful for the histochemical localization 

 of this biologically important substance. 



Lison Modification of Chromaffin Reaction 



SPECIAL REAGENTS 



Formol-Milller Fixative or 5% potassium iodate in 10% formalin. 

 3% Potassium Dichromate or Potassium Iodate. 



