THE CELL 27 



and 3). Sometimes it is obscured by the surrounding proto- 

 plasm. It has a granular appearance, and usually one or 

 ]uore clear refractile bodies — the nucleoli — are seen 

 within it. It stains deeply with many reagents of a 

 basic reaction, such as bjematoxylin, carmine, methylene 

 blue, etc. 



In some cells the nucleus is irregular in shape, and in 

 some it is broken up into a number of pieces, giving the cell 

 a multi-nucleated character. 



It is usualh' composed of (a) fibres arranged in a compli- 

 cated network (fig. 3). These fibres appear to be of two kinds: 

 (1) those forming a fine network — the linin network {G) ; 

 and (2) those forming generally a coarser network, the fibres 

 of which have a special affinity for basic stains — the chromatin 

 network {F). 



The chromatin fibres vary in their arrangement in dif- 

 ferent cells. Usuall}^ they form a network, but occasionally 

 they are disposed as a continuous skein. In nuclei with the 

 former arrangement of fibres, swellings may be observed 

 where the fibres unite with one another — the nodal sivellings, 

 or karyosovie^i, distinct from the nucleolus. The resting 

 nucleus appears to be surrounded by a distinct nit clear 

 membrane, which is either a basket-like interlacement of 

 the fibres at the periphery, or a true membrane produced 

 by adsorption. 



Between the fibres is (h) a more fluid material which may 

 be called the nuclear plasma or Icaryoplasm. Digestion in 

 the stomach removes the nuclear plasma, but leaves the 

 network unacted upon. 



(2) Chemistry. — The nuclear network is composed of 

 Nucleins. These are combinations of protamines (p. 17) 

 with nucleic acid. 



Protamines constitute about one-third and nucleic acid 



about two- thirds of the nucleins. The chief di-amino acid 



in them is Arginin, which constitutes nearly 90 per 

 cent. 



The nucleic acid ma}' be broken down into — 



1. Purins, such as guanin and adenin (see Appendix). 



