2 NUCLEUS 215 



AsTBURY and Bell (1938) proved the existence of a chain lattice with 

 a fibre period of 3.34 A in artificial fibres of Na-nucleate. The degree 

 of polymerization is very high and only by taking special precautions 

 is it possible to isolate them unimpaired from the thymus gland 

 (Knapp, 1946). According to Riley and Oster (195 i), the molecules 

 of concentrated solutions (gels) are arranged in a hexagonal chain 

 lattice. 



The main chain consists chiefly of P- and O-bridges; the phos- 

 phorus carries a free acid group, while the basic groups constitute 

 short side chains. Compared with the nitrogen-containing bases, the 

 dissociation of the phosphoric acid preponderates to such an extent 

 that the system represents a chain of polybasic acids. The isoelectric 

 point lies below p^ 2 (Pischinger, 1937). 



In recent times ribonucleic acid, which does not show the Feulgen 

 nucleal reaction and which was considered to be characteristic for the 

 cytoplasm onlv, has been discovered in the nucleus by UV absorption 

 analvsis. After cell division when the thvmonucleic acid content, as 

 measured by Feulgen colorimetry, drops sharply, the amount of 

 ribonucleic acid increases in the nucleus and may reach nine times 

 that of thymonucleic acid (Ogur, Erickson, Rosen, Sax and Holden, 

 1951). 



b. Fine-Structure of the Nucleus 



The active nucleus. The nucleus possesses for the most part a coarse 

 framework. Its strands are usually of microscopic thickness, but as 

 they are strongly hydrated and insensitive to dyes in the living nucleus, 

 they remain invisible in the ordinary microscope; but they can be 

 detected by the phase contrast microscope, which is an invaluable tool 

 for vital observations in cytology. These framework fibrils have 

 become of great importance, since they could be identified with the 

 uncoiled chromosomes (compare p. 225). A sol-like liquid is found 

 between the strands of the fibrils; it is designated as nuclear sap, 

 karyolymph or enchylema. In other words, the structure is analogous 

 to that of cytoplasm, where the framework of the plasma gel (kino- 

 plasm, spongioplasm) is distinguished from the cytoplasmic sap (para- 

 plasm, enchylema). 



Martens (1927/29) and Pischinger (1937) have elucidated the 

 connection between the invisible fine-structure of living nuclei and 



