ALDEHYDES, NUCLEIC ACIDS, AND PLASMAL 65 



ALDEHYDES, NUCLEIC ACIDS, AND "PLASMAL" 



The research of Feulgen and co-workers (1924,1938,1939) and 

 Imhiiuser ( 1927) led to the demonstration of a loosely bound alde- 

 hyde, "plasmal," in animal tissues. The bound form, "plasmalogen," 

 liberates "plasmal" when treated with mercuric chloride or sub- 

 jected to prolonged acid hydrolysis. The Feulgen reaction, which 

 depends on the formation of a purple-colored compound when alde- 

 hydes react with fuchsin-sulfurous acid, is also given by desoxyri- 

 bonucleic acid (thymonucleic acid) after its purine bases are re- 

 moved by acid hydrolysis, but ribonucleic acid does not give the re- 

 action. The application of the Feulgen reaction to histochemical 

 studies on animal tissues was elaborated by Cowdry ( 1928) and 

 Verne (1928). Milovidov (1938) published a complete bibliography 

 of the 450 papers dealing with the Feulgen reaction up to 1938. Since 

 then Whitaker (1938) described a technique for plant tissues, 

 Stowell (1945a) studied the Feulgen reaction for the photometric 

 measurement of desoxyribonucleic acid (page 126), and Oster and 

 associates (1942,1944) employed the histochemical approach to 

 study tissue aldehydes in sections of fresh frozen material. An im- 

 proved preparation of the Feulgen reagent was reported by Cole- 

 man (1938). Rafalko (1946) claimed that small and diffuse chro- 

 matin elements could be detected with greater delicacy when the re- 

 agent was made by decolorizing a 0.5% solution of the dye by 

 bubbling sulfur dioxide through it. 



The specificity of the Feulgen reaction for aldehydes has been 

 brought up repeatedly. It has been variously claimed that oleic and 

 cinnamic acids give a positive reaction, and that ketosteroids can- 

 not be differentiated from aldehydes by the reaction. Oster and 

 Oster (1946) have examined the question of specificity and have 

 found that the "true" reaction is indeed specific for aldehydes, other 

 carbonyl compounds giving a "pseudo" reaction in certain instances. 

 The differentiation between the "true" and "pseudo" reactions may 

 be made according to Oster and Mulinos ( 1944) x)n the basis that 

 the purple color developed in the former can be decolorized with di- 

 lute sodium hydroxide and restored to its original intensity with 

 hydrochloric acid, while the reddish color of the latter cannot be re- 

 stored by acid after the decolorization. 



