24 



GENERAL SKETCH OF THE CELL 



nuclear substance par excellence, is known as chromatin (Flemmino) 

 on account of its very marked staining capacity wlien treated witli 

 various dyes. In some cases the chromatin forms a nearly continu- 

 ous network, but it often appears in the form of more or less detached 

 rounded granules or irregular bodies. The second constituent is a 

 transparent substance, invisible until after treatment by reagents, 



known as linin (Schwarz). This 

 substance, which is probably of 

 the same nature as the cyto- 

 plasmic network outside the 

 nucleus, surrounds and supports 

 the chromatin, and thus forms 

 the basis of the nuclear net- 

 work. 



c. The nucleoli, one or more 

 larger rounded or irregular 

 bodies, suspended in the net- 

 work, and staining intensely 

 with many dyes ; they may be 

 absent. The bodies known by 

 this name are of at least two 

 different kinds. The first of 

 these, the so-called true nucleoli 

 or plasmosovics (Figs. 5, 7, B, 

 10), are of spherical form, and 

 by treatment with differential 

 stains such as ha;matoxylin and 

 eosin are found to consist typi- 

 T- k'^,'-m°'~T"° ""'''" ^'■°'" ^'^'^ ">'P'^ °^ cally of a central mass stainino- 



Lieberkuhn in the salamander. [Heidenhain.I in,/ <-! >. i ^ 



The character of the chromatin-net.ork , ^^'^ Cytoplasm, SUrrOUuded 



(^a«c/zw;«a//«) is accurately shown. The upper '^Y ^ shell which Staius like 



nucleus contains three plasmosomes or true chromatin. Those of the Other 



nucleoli ; the lower, one. A few fine linin-threads r "J. c ui uic OLUer 



(oxychromathi) are seen in the upper nucleus lOrm, the " Uet-kuotS " (NetZ- 



running off from the chromatin-masses. The \x\Ol<in),OX karvosomcs, 2,XQ ^Wh&r 



clear spaces are occupied by the ground-sub- u • i ■ '^•', 'ti c ciLiier 



stance. Spherical or irregular in form, 



stain like the chromatin, and 

 appear to be no more than thickened portions of the chromatic 

 network (Figs. 5, 7, A, 10). Besides the nucleoli the nucleus may 

 m exceptional cases contain the centrosome (p. 225), which has 

 undoubtedly been confounded in some instances with a true nucleolus 

 or plasmosome.i There is strong evidence that the true nucleoli are 



1 Flemming first called attention to the chemical difference between the true nucleoli and 

 the chromatic reticulum ('82, pp. 138, 163) in animal cells, and Zacharias soon afterwards 

 Studied more closely the difference of staining-reaction in plant-cells, showing that the 



