the nucleic acid content of tissues and -cells 7 



3. Procedure of Ogur and Rosen (1950) 



This method^* (Table I) was developed to deal with the problem of de- 

 termining PNA and DNA in amounts as low as 1 ng. in plant root tips and 

 pollen cells. Because of the small amounts of material available and the 

 presence of interfering substances (pentosans, polyuronides), both the 

 Schmidt and Thannhauser and the Schneider procedures were considered 

 inadequate for the purpose. 



The preliminary extraction of the tissue begins with alcohol treatment 

 (XI and XII) in order to eliminate as soon as possible an alcohol-soluble 

 compound which gives an intense purple coloration with diphenylamine. 

 The overnight treatment of tissue residue XIV at 4° with A'' PCA extracts 

 only PNA, but repeated extractions may be necessary when the PNA/DNA 

 ratio is high. In this fraction (XV) PNA is measured by ultraviolet absorp- 

 tion at 260 m/i or on the basis of its P content. 



The DNA is subsequently extracted from the tissue residue by hot acid 

 treatment (XVI) and can be determined by the diphenylamine reaction, ^^ 

 ultraviolet absorption at 270m/i, or the P content of the fraction. In plant 

 material, about 3 % of the total P remains in the final residue. 



The method is not equally effective with all tissues. Patterson and Dackermann^' 

 could get only partial extraction of PNA from Drosophila salivary glands, and Ogur 

 et al^^ report that in 3'east cells part of the DNA is extracted during cold PCA treat- 

 ment. Koenig and Stahlecker" applied a modified procedure to fixed tissue sections 

 from mammalian liver and nerve tissue. In certain species of bacteria 30 hrs. of ex- 

 posure to PCA was needed to remove all the PNA.''* 



III. Normal Adult Tissues 



Very often in the literature the terms "content" and "concentration" 

 are employed as synonyms, when, in fact, they should refer to two distinct 

 features. In this review the term "content" will be used only when results 

 are given as amounts per organ or as amounts per cell. The term "concen- 

 tration" will be confined to describing amounts per unit weight of tissue or 

 per unit of protein nitrogen. 



Information on the amounts of PNA-P and DNA-P in normal adult tis- 

 sues is collected in Table II (rat tissues) and Table III (other animals and 

 man). More data are available for the rat than for any other animal, and 

 the average amounts of DNA-P per nucleus have been carefully determined 

 in a number of adult rat tissues. ^^ Owing to the high proportion of polyploid 

 nuclei in rat liver, the average amount of DNA-P per nucleus is higher in 

 liver than in any other tissue (Table II). This point is discussed in detail in 

 Chapter 19. 



^5 H. Koenig and H. Stahlecker, /. Natl. Cancer Inst. 12, 237 (1951) . 

 ^8 W. A. Cassel, J. Bacteriol. 59, 185 (1950). 



