THE CELL. 23 



solutions, and is dissolved in stronger solutions. The 

 unchanged nucleolus becomes even plainer after such treat- 

 ment. Nuclein is colored better in acid stains, while para- 

 nuclein takes up more readily basic stains, eosin, and fuchsin. 

 In this way these two parts can be differentiated by the so- 

 called double staining. 



3. Linin takes part in the formation of the network or 

 framework. It is not stained by the ordinary coloring 

 materials, and forms the so-called achromatic constituent of 

 the nucleus. 



4. Lantanin occurs often in the linin in the form of fine 

 granules, which may be stained by acid anilin dyes, as opposed 

 to chromatin, which takes up only basic anilin-stains. Lan- 

 tanin is therefore called oxychromatin, while chromatin is 

 known as basichromatin. 



5. Nuclear fluid (Kernsaft) fills out the spaces between the 

 structures formed of nuclein, paranuclein, and linin. 



6. Amphipyrenin is the substance which forms the nuclear 

 membrane separating the nuclear space from the protoplasm. 

 In large nuclei the nuclear membrane shows a plainly double 

 contour. In chemical properties it is most nearly related to 

 pyrenin. 



The nucleus may be simple or complicated in form. The 

 most simple structure is seen in those nuclei which consist of 

 quite compact nuclein bodies (e. g., spermatozoa). In other cases 

 the nucleus has a more open structure, the spaces in the nuclear 

 network being filled with nuclear fluid. Such a nuclear net- 

 work may in its simpler forms be made up only of chromatin ; 

 in other cases linin and lantinin are also present (Figs. 1 and 2). 

 The resting nucleus may in certain cases appear as a vesicle 

 surrounded by a nuclear membrane (amphipyrenin). In this 

 is to be found a network of nuclein (chromatic) and linin 

 (achromatic), in which granules of lantanin are scattered. It 

 contains also a nucleolus (paranuclein) and a nuclear fluid. 



The third but unessential constituent of the cell, the cell skin 

 or cell membrane, may often be lacking in animal cells. If the 

 superficial layer of the protoplasm is distinguished from the 



