24 C. L. SADRON 



TABLE I 



Molecular Weights (M w ) and Intrinsic Viscosities ([rj]) 



of DNA from Calf Thymus 



Methods of Preparation 



1 R. Signer and H. Schwander, Helv. Chim. Acta 32, 853 (1949). 



2 M. G. Sevag, D. B. Lackman, and J. Smolens, J. Biol. Chem. 124, 425 (1938). 



» A. M. Marko and J. A. V. Butler, J. Biol. Chem. 190, 165 (1951). E. R. M. Kay, N. S. Simmons, and A. 

 L. Dounce, J. Am. Chem. Soc. 74, 1724 (1952). 



« J. A. V. Butler, D. W. F. James, and B. E. Conway, Trans. Faraday Soc. 50, 612 (1955). 



5 K. S. Kirby, Biochem. J. 66. 495 (1957). 



Authors 



° J. Hermans and J. Pouyet, published in Thesis of J. Hermans, Jr., Leiden (1958). 



6 R. Vendrely, C. R. M., Strasbourg. 



c J. Hermans, Laboratory of Physical Chemistry, University of Leiden. 

 d J. P. Coelingh, Laboratory of Biochemistry, University of Leiden. 

 * J. A. V. Butler, Chester Beatty Research Institute, London. 



1. With a given material (calf thymus, hen erythrocytes, etc.) a given 

 procedure of extraction gives a sample belonging to group I or to group II, 

 without any apparent reason. 



2. At least with samples of group II, the values of M w depend on the con- 

 centration of NaCl in the solution, and — if precipitation of DNA by ethanol 

 has taken place — of the NaCl concentration of the initial solution. Curves 

 I and II of Fig. 10 illustrate the results obtained by Pouyet on a sample 



20 J. Pouyet, unpublished (1957). 



