66 HEWSON SWIFT 



NH 



OH \/ OH 



RC02SHN<^ >— C— ^ SnHSO.CR 



H H 



This must combine with two aldehyde groups to restore the quinoid struc- 

 ture associated with the colored compound. Postulated intermediate steps 

 were (1) the coupling of one aldehyde group with the sulfinic group of 

 fuchsin-sulfonic acid, (2) the change of another amino group into a sul- 

 finic group, and (3) the coupling with a second aldehyde, and consequent 

 release of the sulfonic acid group from the central carbon. The aldehyde- 

 Schiff complex produced is obviously a different dye than the original basic 

 fuchsin, as may be shown by absorption curves of tissues.®^ It is readily 

 distinguished by its magenta, rather than red, coloration. 



The Feulgen reaction typically shows two absorption maxima (Fig. 4) 

 denoting the presence of two chromophores, and under different conditions 

 of staining these two components may vary independently. Since acidic 

 solutions of basic fuchsin are also capable of combining with aldehyde 

 groups,^^''''' presumably through some type of amino-aldehyde linkage, it 

 seems possible that recoloration may proceed through combination of the 

 tissue aldehyde groups with either the amino or sulfinic groups of the 

 leucofuchsin molecule. 



As mentioned by Conn,^^ commercial samples of basic fuchsin show some 

 variation, most being mixtures both of pararosaniline (triaminotriphenyl- 

 methane acetate) and its mono- or dimethyl derivatives. The compound 

 nature of the preparations does not seem to interfere with their stainability, 

 although for quantitative work it is probably best to obtain pararosaniline, 

 in as pure form as possible. Preparation of the Schiff reagent has been 

 carried out in many different ways.''-"^^ Although the source of SO2 does 

 not seem of much consequence, the amount present in the reagent can 

 affect its sensitivity (see below). The fuchsin-sulfonic acid, once formed, 



«8 R. E. Stowell and V. M. Albers, Stain Technol. 18, 57 (1943). ' 



69 E. D. DeLamater, Stain Technol. 23, 161 (1948). 



^^ G. Gomori, "Microscopic Histochemistry." Univ. of Chicago Press, Chicago, 1952. 



^1 H. J. Conn, "Biological Stains," 6th ed. Biotech. Publications, Geneva, N. Y. 

 1953. 



" W. B. Atkinson, Stain Technol. 27, 153 (1952). 



^^ R. L. Shreiner and R. C. Fuson, "The Sj'stematic Identification of Organic Com- 

 pounds." Wiley, New York, 1940. 



" J. D. Barger and E. D. DeLamater, Science 108, 121 (1948). 



