26 CELLS AND EXTRACELLULAR ELEMENTS. 



human leukocytes ; and e-granules, fine neutrophilic granules 

 (by some considered oxyphilic), very common in human leu- 

 kocytes. 



The nucleus : Most cells contain in their interior a nucleus, 

 a rounded structure distinctly marked off from the cell-body. 

 It appears especially prominent when stained by nuclear and 

 basic dyes, which impart to the nucleus a deep color, while 

 the body of the cell is colored little or not at all. Nuclei are 

 inclosed and separated from the rest of the cell by a mem- 

 brane, the nuclear membrane. The nucleus consists of two 

 portions: the nuclear fibrils, or reticulum, a network of fibers; 

 and the nuclear matrix, a semifluid substance in the meshes 

 of the reticulum. 



The fibrillar substance, again, is composed of two parts, a 

 homogeneous ground-substance called linin, supported in 

 which are granules, fibres, and filaments of a substance called 

 chromatin. In stained specimens the deep color shown by the 

 nucleus is taken by the chromatin (whence the name), while 

 the ground-substance, or limn, and the nuclear matrix are less 

 colored. 



From the phenomena of karyokine&is, the chromatin is sup- 

 posed to be of the highest significance and importance in vital 

 phenomena, especially in connection with reproduction and 

 heredity. Chromatin has been conjectured to be identical 

 with nuclein, a chemical constituent of cells which is regarded 

 from physiological and chemical considerations as playing a 

 highly important part in the economy of cell-activity. 



In many cases, as in ova and nerve-cells, the nucleus con- 

 tains a little nucleus of its own, or more than one, called the 

 nucleolns. Most cells are uninucleated, or contain but a single 

 nucleus each ; certain classes of cells, however, arc multinu- 

 cleated, containing several or numerous nuclei each, as the 

 voluntary muscle-cells, osteoclasts, and the giant cells present 

 in certain pathological processes. 



In shape, the nuclei are usually spheroidal, oval, or discoid ; 

 but in different cases the shape varies greatly, and may be ex- 

 ceedingly irregular. 



The location of the nuclei in the cells varies, being some- 

 times in (he centre, sometimes excentric, sometimes at the very 

 periphery of the cell. 



