THE DEOXYRIBONUCLEIC ACID CONTENT OF THE NUCLEUS 161 



deoxypentose, found in a single sea urchin egg more than a hundred times 

 as much DNA as in the sperm [Arhacia sperm, 21 to 30 pg., egg, 600 to 

 1000 pg.^^ Arhacia aequituberculata sperm, 0.67 pg.,egg, 220 pg.; Paracen- 

 trotus lividus sperm, 0.70 pg.^^]. These results are probably due to unavoid- 

 able interference by the enormous amount of cytoplasmic substance in the 

 estimation of the very small quantity of DXA of the nucleus. But even 

 more precise methods, such as the microbiological technique used by Hoff- 

 J0rgensen and Zeuthen,^^"^- working on Rana platyrrhina, and the micro- 

 biological determinations of thymine made by Elson and Chargaff ^^ on Para- 

 centrotus, yield values for DNA which are still too high (Paracentrotus 

 lividus sperm, 1.0 to 1.1 pg., egg, 24 to 26 pg.). As Zeuthen^i points out, the 

 total amount of DNA found in the frog's egg (0.65 jug-, 5000 times more than 

 in the sperm) could not be contained in the nucleus even if it consisted only 

 of a solid mass of DNA. The possibility of extranuclear DNA in eggs must 

 therefore be considered, and the presence of DNA stbred in the egg cyto- 

 plasm for use in subsequent mitoses is now admitted-^' -2. 24. cytochemical 

 and biochemical evidence of DNA in the cytoplasm has been provided in 

 several instances.^^"-* This assumption, however, cannot be accepted with- 

 out reserve, for the egg cytoplasm is generally Feulgen-negative. We must 

 therefore suppose the extranuclear DNA to be in a very dilute state in the 

 cytoplasm and below the limits of stainability; or, alternatively, it may be 

 a precursor of DNA, nonstainable by the Feulgen reaction. This very in- 

 teresting point needs further investigation and could throw some light on 

 the question of the synthesis of DNA during the first stages of development. 



The chemical determination of the DNA content of the nuclei of plant 

 tissues is not easy because the isolation of nuclei is particularly difficult in 

 such material ; only the gametes can be studied easily .^^ Heagy and Roper'" 

 examined the DNA content of conidia of diploid and haploid strains of 

 Aspergillus nidulans. They found in diploid strains 9.39 and 7.75 pg. of 

 DNA for 10^ conidia and in haploid strains 4.04 and 4.22 pg. for 10^ co- 

 nidia, i.e., approximately half the content of diploids. 



In conclusion, the chemical method for determining the DNA content of 



«» C. Vendrely and R. Vendrely, Cnmpt. rend. soc. hiol. 143, 1386 (1949). 

 21 E. Hoff-J0rgensen and E. Zeuthen, Nature 169, 245 (1952). 

 " E. Zeuthen, Puhhl. staz. zool. Xapoli 23, Suppl. 2, 59 (1952). 

 " D. Elson and E. Chargaff, Experientia 8, 143 (1952). 

 2^ A. W. Pollister, Exptl. Cell. Research 3, Suppl. 2, 59 (1952). 

 " F. Schrader, Science 114, 486 (1951). 



2« A. H. Sparrow and M. R. Hammond, .4m. /. Botany 34, 439 (1947). 

 " N. Fautrez-Firlefyn, Compt. rend. soc. hiol. 144, 1127 (1950). 

 " H. Fraenkel-Conrat and E. D. Ducay, Biochem. J. 49, Proc. xxxix (1951). 

 "M. Ogur, R. O. Erickson, G. Rosen, K. B. Sax, and C. Holden, Exptl. Cell Re- 

 search 2, 73 (1951). 

 30 F. C. Heagy and J. A. Roper, Nat^lrc 170, 713 (1952). 



