52 INTRODUCTION TO CYTOLOGY 



of the nuclei in merogonic echinoderm larvae is dependent upon the num- 

 ber of chromosomes each contains. In a more extended study (1905) he 

 demonstrated that it is the surface of the nucleus that is proportional 

 to the chromosome number, and also that the size of the cell is propor- 

 tional to both. Gates (19096), however, adduced evidence to show that 

 this rule is by no means universal. This question has been investigated 

 in connection with studies on polyploid plants with the general result 

 that, although in the majority of cases a rise in the chromosome number of 

 a species is seen to be accompanied by an increase in nuclear and cell 

 size, there are cases in which such a change in related types seems to have 

 been accompanied rather by a decrease in the size of the chromosomes. 

 This indicates that it is volume of karyotin, and not mere number of 

 chromosomes, that is of importance in this connection (see Tischler, 

 1921-1922, pp. 588^.). 



With respect to the physical nature of the nucleus as a whole, studies 

 with the micromanipulator have shown^ that it ordinarily consists, at 

 least in part, of an elastic gel having a higher viscosity than that of the 

 cytoplasm, often being so firm that it can be handled without injury by 

 the instrument. This obviously would be impossible were the nucleus 

 merely a watery droplet or vesicle in the cytoplasm. The germinal 

 vesicle (nucleus) of certain animal eggs Chambers finds to be a sol droplet 

 with a gel membrane; when pinched in two by the instrument the two 

 halves will reunite if they come in contact. 



Studies on the electrical properties of cells have shown that the 

 nucleus is apparently negative to the cytoplasm. Free nuclei and the 

 heads of spermatozoa, which are composed almost entirely of nuclear 

 material, pass to the anode in an isotonic cane-sugar solution; whereas, 

 cells rich in cytoplasm, such as large leucocytes, pass to the cathode. ^° 

 The difference in electrical potential ,on the two sides of the nuclear 

 membrane may be of considerable significance in the vital processes. 



The chemical nature of the nucleus has been touched upon in the 

 preceding chapter (p. 26). The exact nature and distribution of the 

 various constituents are not well known, but recent researches'^ seem to 

 show that the reticulum contains both nucleo-protein and lipide, the 

 latter being in part combined with protein, while the karyolymph con- 

 tains lipides but no nucleo-protein. The most nearly specific test so 

 far devised for the chromatic nucleo-protein ("chromatin") of nuclei 

 is the Feulgen reaction, in which the production of a purplish color in 

 decolorized basic fuchsin indicates the presence of thymonucleic acid.'^ 



8 Kite (1913), Chambers (1914, 1917, 1921), Seifriz (1926c). 

 i« R. S. Lillie (1903), Hardy (1913). 



11 Nemec (1909, 1910), Hansteen-Cranner (1919), Grafe (1925), Grafe and Magis- 

 tris (1926), Wermel (1927), Gutstein (1927), Shinke and Shigenaga (1933). 



12 Feulgen and Rossenbeck (1924), Feulgen (1926). See also McClung's Micro- 

 scopical Technique and Margolena (1932). 



