334 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 2 



narrower limits : ( 1) at 2600 A. absorption of the pyrimidine or purine 

 ring of the two nucleic acids occurs; (2) at 2800 A. there is found the 

 maxima in absorption of the aromatic amino acids. 



Ultraviolet methods, when properly controlled, give a measure of 

 the total nucleic acids, but the two main types (UNA and DNA) can 

 be distinguished only by removing one or the other through treatment 

 with a specific nuclease. There has been considerable controversy 

 about the ultraviolet absorption of living cells ; e. g., it has been found 

 that the amount of absorption increases with the length of exposure. 

 Commoner and Lipkin (1949) raised the question as to the degree of 

 orientation of the nucleic-acid molecule. If the molecules are ori- 

 ented, is the orientation sufficient to invalidate the quantitative data 

 so obtained? A second probable source of error lies in the danger 

 of light scattering, which Casperson (1947) has discussed in detail. 

 In view of the above factors one should accept with caution any 

 theories based on their quantitative value. This conclusion does not 

 mean that ultraviolet spectroscopy is without value, since qualita- 

 tively the information is invaluable. 



Chemically the nucleic acids can be identified and localized by: 

 (1) the Feulgen reaction, (2) basic staining, and (3) Brachet's ribo- 

 nuclease technique. 



Feulgen and Rossenbeck (1924) adapted the Schiffs-base reaction to 

 cytology for the visual identification of desoxyribose nucleic acid. 

 Under proper controls this procedure is qualitatively specific, though 

 there is little to support its quantitative value. The extensive litera- 

 ture on the subject has been reviewed by Stowell (1945) and Lumb 

 (1950). The latter author in the same paper critically analyzed all 

 the more commonly used nucleic-acid techniques. 



Of equal importance are the methods for the detection and localiza- 

 tion within the cell of various types of enzymes. Most techniques 

 of this sort involve incubation of the cellular material in a suitable 

 substrate solution, with the production at the site of enzymatic activity 

 of a colored substance or of a substance which can be converted into a 

 colored compound. There are tests of this nature for the localization 

 of cytochrome oxidase, peroxidase, amino oxidase, lipases, proteases, 

 glucoronidase, phosphorylase, alkaline and acid phosphatase, and 

 others. None of these techniques, with the exception of alkaline 

 phosphatase has been subjected to a critical analysis. Danielli (1946) 

 established the validity of the alkaline-phosphatase technique when 

 properly controlled. A detailed account of the possible significance of 

 the alkaline-phosphatase enzyme to nucleic acid and protein metab- 

 olism and the process of calcification is to be found in J. R. G. Brad- 

 field's recent review article, "The Localization of Enzymes in Cells" 

 (1950). For procedures, consult Glick's (1949) book, "Techniques 

 of Histo- and Cyto-chemistry." 



