Feulgen Reaction 293 



Among the nucleic acids, oxidation ^vill not form aldehydes and acid 

 hydrolysis is required. The two kinds of nucleic acid are (1) thymo- 

 nucleic acid (desoxyribose or deoxyribose nucleic acid, desoxypentose 

 or deoxypentose ribonucleic acid, or DNA), the principle component of 

 nuclei and containing desoxyribose (desoxypentose) sugar; and (2) 

 ribose nucleic acid (pentose nucleic or plasmo nucleic acid, or RNA), 

 fotmd in cytoplasmic structures, with ribose (pentose) as the sugar com- 

 ponent. When nucleic acids are treated with warm HCl, aldehyde 

 groups are released from the desoxypentose sugars, but not from the 

 pentose sugars. Thus, when treated with Schiff reagent, DNA reacts 

 positively, but RNA reacts negatively. Both, however, can be demon- 

 strated at the same time by selective dyeing with pyronin and methyl 

 green (page 297). 



Schiff's reagent. In an acid solution and with excess of SOo present, 

 basic fuchsin (a mixture of several related phenyl methane dyes, ro- 

 sanilins, and pararosanilins built on the quinoid ring) is reduced to 

 form a colorless N-sulfinic acid (fuchsin sulfurous acid). This reagent, 

 with the addition of aldehydes, forms a new phenyl methane dye, 

 slightly different from basic fuchsin since the color is more purple-red 

 than pure red. The chemical reaction is not wholly vniderstood. Thus, 

 areas rich in DNA, after hydrolysis, show deep coloration. Schiff's is 

 stable so long as an excess of SOo is present and high acidity. Anything 

 removing these conditions restores the original dye and produces a 

 pseudo-reaction. But Avhen regenerated by an aldehyde, the dye be- 

 comes extremely resistant to such agents. Schiff's reagent is not a dye; it 

 lacks a chromophore and is, therefore, colorless. Baker (1958) considers 

 this an example of localized synthesis of a dye; when the Schiflf's (color- 

 less) comes in contact with an aldehyde, the chromophore of the triaryl- 

 methane (quinoid ring structure) dye is reconstituted. The additive 

 compound of the aldehyde with the Schiff could be called a dye. 



Schiff's deteriorates rapidly at temperatures over 40°C, but at 0° 

 and — 5°C, if kept tightly stoppered, the deterioration is slow. Under 

 these conditions it will keep as long as six months. 



References: Atkinson (1952); Baker (1958); Bensley (1959); Glegg, 

 Clermont and Leblond (1952); Gomori (1952); Lhotka and Davenport 

 (1949); Lillie (1951A, 1953, 1954A and B); and Stowell (1945). 



Feulgen Reaction 



fixation: one containing HgClo is preferred. 



