162 R. VENDRELY 



the nucleus has been appHed generally with success to adult tissues where 

 the rate of mitosis is negligible, and to sperm cells. 



b. Results of Histophotometry in Visible Light 



The method of cytophotometry was described as early as 1947 but cy to- 

 chemical determinations on nuclei could not be,^^ regarded as reliable until 

 they were checked against a chemical procedure. The demonstration of the 

 constancy of DNA in diploid nuclei by chemical methods gave a standard 

 of comparison and permitted a rapid development of the cytophotometric 

 method for the study of a great number of problems. The first cytophoto- 

 metric studies confirmed the chemical values for the constancy of DNA and 

 its relationship with the number of chromosomes.^^ This work was per- 

 formed by the school of Pollister (Ris, Leuchtenberger, Swift, Alfert) with 

 the apparatus described by Pollister and Moses.^* Another apparatus for 

 cytophotometry based upon the same principle was built in Belgium by 

 Pasteels and Lison,^'' whose results have sometimes been in disagreement 

 with those of the American workers, as we shall see later. 



Cytophotometric measurements do not permit of a quantitative deter- 

 mination of the DNA content of the nucleus in absolute units, but it is pos- 

 sible to calculate absolute values from the amount in arbitrary units using, 

 as a standard, nuclei of known DNA content treated together with the 

 unknown. ^^ In practice, this calculation is of no great interest. 



Ris and Mirsky^- showed the existence in rat liver of three classes of 

 nuclei, the ratio of intensity of the Feulgen reaction being very close to 

 1:2:4. This occurrence of polyploidy has been confirmed and studied on 

 other organs and other species by Swift,^^ by Pasteels and Lison,^^ by 

 Leuchtenberger and the Vendrelys,^® and by Davidson." 



It would seem generally that an increase in the size of the nucleus is correlated with 

 an increase of the number of chromosomes and consequently with an increase of the 

 DNA content of the nucleus. ^^ But Schrader and Leuchtenberger^' showed that in the 

 insect Arvelius the DNA content of the nucleus is the same in three types of spermato- 

 cytes, the nuclear volumes of which were 200, 400, and 1600 cubic microns, respec- 

 tively. Leuchtenberger and Schrader^^ showed also in rat liver this independence of 

 the DNA from the nuclear volume. 



'1 A. W. Pollister and H. Ris, Cold Spring Harbor Symposia Quant. Biol. 12, 147 



(1947). 

 32 H. Ris and A. E. Mirsky, J. Gen. Physiol. 33, 125 (1949). 

 3' A. W. Pollister and M. J. Moses, /. Gen. Physiol. 32, 567 (1949). 

 '* L. Lison, Acta Anat. 10, 333 (1950). 

 '5 H. H. Swift, Physiol. Zool. 23, 169 (1950). 

 '« J. Pasteels and L. Lison, Conipt. rend. 230, 780 (1950). 

 " J. N. Davidson, Bull. soc. chim. biol. 35, 49 (1953). 

 38 F. Schrader and C. Leuchtenberger, Exptl. Cell Research 1, 421 (1950). 

 " C. Leuchtenberger and F. Schrader, Biol. Bull. 101, 95 (1951). 



