544 G. H. BEAVEN, E. R. HOLIDAY, AND E. A. JOHNSON 



the views of Commoner and Lipkin and concludes with Thorell and Ruch 

 that errors due to orientation would only be serious in biological material 

 of exceptional character, in which the degree of orientation is very high. In 

 spite of considerable debate^^^ it does not appear that Commoner and 

 Lipkin 's arguments have been completely refuted, however, and it seems 

 likely that more experimental work on carefully chosen specimens will be 

 necessary to resolve this issue. 



7. DicHROiSM OF Stained Nucleic Acids 



The combination of a dye with an oriented macromolecule may lead to 

 orientation of the dye molecules, causing the visible light absorption of the 

 dyed macromolecule to show dichroism. There is an extensive literature on 

 the visible dichroism of substantively dyed cellulose fibers, and White and 

 Elmes^"*^ have made some observations on dyed birefringent fibers of DNA 

 and the corresponding nucleoproteins isolated from various human tissues. 

 With pyronine and methyl green, the positive dye dichroism indicates that 

 the absorbing groups of the dyes lie parallel to the fiber axis, although 

 imperfectly oriented. For toluidine blue-stained fibers the visible dichroism 

 is negative, and the absorbing groups of the dye appear to lie roughly at 

 right angles to the fiber length. It is of interest to note that the oriented 

 DNA fibers used in this work were laid down within crystals of sodium 

 chloride depositing from solutions of the nucleic acid or nucleoprotein in 

 sodium chloride solutions. The salt could be dissolved away with methanol 

 leaving arrays of birefringent fibers which show the type A-type B inter- 

 conversions described by Wilkins et alP'' The dye dichroism of stained, 

 oriented nucleic acid is of great interest in relation to the use of methyl 

 green as a specific dye for high-molecular- weight DNA; conversely pyro- 

 nine stains depolymerized DNA and undegraded PNA. The differential 

 staining of tissues by methyl green-pyronine (Unna-Pappenheim) is thus 

 intimately related to the nature and state of the nucleic acids present. ^^^ 

 The subject has been discussed in detail by Kurnick"* and Thomas."^ The 

 phosphate groups are certainly implicated in the binding of basic dyes 

 by nucleic acids,^*^ but an explanation for the binding of specific dyes in 

 terms of dye molecular structure has not yet been attempted. It is perhaps 



1" B. Commoner, Discussions Faraday Soc. No. 9, 393 (1950); H. R. Catchpole and 



I. Gersh, ibid., p. 471. 

 "2 J. C. White and P. C. Elmes, Nature 169, 151 (1952). 

 1" J. Brachet, Compt. rend. soc. biol. 133, 88 (1940). 

 1" N. B. Kurnick, Exptl. Cell Research 1, 151 (1950) ; ibid. 3, 649 (1952) ; Stain Technol. 



27, 233 (1952); Arch. Biochem. 29, 41 (1950). 

 1" R. Thomas, Arch, intern, physiol. 61, 270 (1953). 

 1" L. F. Cavalieri and A. Angelos, /. Am. Chem. Soc. 72, 4686 (1950) ; L. F. Cavalieri, 



S. E. Kerr, and A. Angelos, ibid. 73, 2567 (1951). 



