CHAPTER 19 



The Deoxyribonucleic Acid Content of the Nucleus 

 R. VENDRELY 



I. Introduction 155 



II. The DNA Content of the Nucleus 157 



1. The DNA Content of the Nucleus in the Various Tissues of the Same 

 Animal 157 



a. Chemical Measurement of the DNA Content of the Nucleus in the 

 Somatic Cells and Gametes 157 



b. Results of Histophotometry in Visible Light 162 



c. Quantitative Photometry in Ultraviolet Light 164 



2. The DNA Content of the Nucleus in Different Species of Animals . . 165 



III. Can the DNA Content of the Nucleus Be Considered as a "Constant"? . . 168 



1. Interpretation of the Idea of Constancy in Biology 168 



2. Possible Variations of the DNA Content of the Nucleus 171 



a. DNA and Polyteny 171 



b. Pollen Formation 172 



c. DNA and Metabolism 172 



3. The DNA Content of the Nucleus in Dividing Cells 173 



a. Preparation for Mitosis and Meiosis 173 



b. DNA Content of Nuclei in Embryonic Tissues and in Tissue Cul- 

 tures, and the Problem of Differentiation 175 



IV. Conclusion 176 



I. Introduction 



Deoxyribonucleic acid (DNA) has been kno^vn for a long time as an essen- 

 tial component of the chromatin of cell nuclei. Cytochemists, using the 

 specific Feulgen reaction, and biochemists, analyzing isolated nuclei and 

 cytoplasmic elements, have sho^vn that DN^A is strictly confined to the nu- 

 cleus and that all nuclei contain DNA. 



In an attempt at a quantitative approach, the classical histologists des- 

 cribed differences in stainability in nuclei from various tissues in different 

 physiological states, but few of them used the specific Feulgen reaction. 

 Even when they did, they could appreciate with the eye merely the density 

 of Feulgen stain in the nucleus rather than the total amount of staining 

 material (for the determination of which the total volume of the nucleus 

 must be known). More recent studies by biochemists have provided a better 

 approach to the problem of the DNA content of the nucleus. They pointed 



155 



