68 HEWSON SWIFT 



groups, since aldehyde coupling reagents, such as bisulfite,^^ semicarbazide, 

 phenyl hydrazine, hydroxylamine,^" and cyanide,^'' greatly reduce the in- 

 tensity of the reaction provided they are used after hydrolysis. Agents 

 which esterify the aldehyde or change it to an alcohol also block the reac- 

 tion.^^ Also some other reactions for aldehydes give a positive test for 

 nuclei after hydrolysis, for example, silver ammoniac solutions*- and hydra- 

 zine.*'-*^ Other aldehyde tests may fail to react. *^ 



Why aldehyde groups should be produced by DNA and not PNA is not 

 altogether clear. It has been pointed out by several workers*^ that acid 

 hydrolysis removes most PNA from tissues. The specificity cannot rest on 

 this alone, however, as intimated by Carr,** since PNA in vitro is also com- 

 pletely negative. Feulgen and Rossenbeck^^ demonstrated that the purine- 

 sugar bond of DNA was split in hydrolysis to liberate the aldehyde, and 

 suggested that the PNA purines were not so readily liberated. Overend and 

 Stacey*^ synthesized a number of normal and deoxysugars in both pyranose 

 and furanose forms. They reported that some sugars may occur naturally 

 in a noncyclic aldehydo form and that this was present in significantly 

 greater amounts in deoxyfuranose sugars than in those with a deoxypyra- 

 nose or normal furanose structure. According to this view, the hydrolysis 

 makes the aldehyde groups available both through rupture of aldehydo 

 bonds involved in polymerization, and also by the liberation of purines. 



A properly performed Feulgen reaction is practically specific for DNA, 

 as has been demonstrated by many workers. DNA removal, through the 

 use of purified pancreatic deoxyribonuclease prepared according to 

 McCarty,** will render a tissue Feulgen-negative, while prolonged trypsin 

 digestion, though it may destroy the integrity of the tissue, has little effect 

 on the Feulgen intensity of remaining tissue fragments.*^ A number of 

 investigators have tested Feulgen specificity with drops of DNA- or PNA- 

 protein mixtures on slides.'"''*'' These tests also demonstrate that proteins, 

 and PNA from yeast, liver, or tobacco mosaic virus are completely Feulgen- 

 negative. 



There are a few other substances occurring in tissues that are likely to 



"J. Brachet, Experientia 2, 142 (1946). 



80 M. A. Lessler, Arch. Biochem. and Biophys. 32, 42 (1951). 



81 J. F. Lhotka and H. A. Davenport, Stain Technol. 26, 35 (1951). 

 «" R. Feulgen and K. Voit, Z. physiol. Chem. 137, 272 (1924). 



83 E. Herman and E. W. Dempsey, Slain Technol. 26, 185 (1951). 



" A. G. E. Pearse, J. Clin. Pathol. 4, 1 (1951). 



«s J. O. Ely and M. H. Ross, Anat. Record 104, 103 (1949). 



86 J. G. Carr, Nature 156. 143 (1945). 



"W. G. Overend and M. Stacey, Nature 163, 538 (1949). 



88 M. McCarty, Bacterial. Revs. 10, 63 (1946). 



89 D. G. Catcheside and B. E. Holmes, Symposia Soc. Exptl. Biol. 1, 225 (1947). 



