THE MITOTIC CYCLE 



isolated nuclei by Vendrely and Vendrely^^ and Davidson and 

 McIndoe^^ suggest ratios of DNA/RNA of 3-30 times. It is probable 

 that if the DNA were not scattered in small aggregates throughout the 

 nucleus it would appear to be much greater in amount. In the rat liver 

 nucleus, however, Bounce et aliP^ find more RNA than DNA. 



Within the last two years results of much interest have been obtained 

 by estimation of the absolute quantity of deoxyribonucleic acid in the 

 nucleus. Where bulk chemical methods have been used, nuclei has 

 been isolated either by the citric acid procedure or by the anhydrous 

 technique of Behrens (Dounce et alii^^). Their density in a suspension 



Table II. DNA CONTENT OF NUCLEI IN mg X 10 « 



is measured by counting on a haemocytometer slide, and the prepara- 

 tion is then analysed in bulk for DNA. Boivin, Vendrely and Ven- 

 drely, 2^ 2^ MiRSKY and Ris^° and Davidson and McIndoe^' have all 

 made measurements of this kind on various types of nucleus; some of the 

 values obtained are here reproduced in Table II, together with estimates 

 made by other methods which will shortly be described.* 



The agreement between the results obtained on vertebrate tissues by 

 the different authors at first was considered to be sufficient to support 

 these generalizations: 



1. The DNA content of a nucleus is characteristic of the species and 

 is constant from tissue to tissue. 



2. Diploid and somatic nuclei have approximately twice the DNA 

 content of the haploid sperm nucleus. 



* MiRSKY and Ris'"* have recently published a further series of estimations of nuclear 

 DNA, in both vertebrates and invertebrates. 



34 



