2 4 



GENERAL SKETCH OF THE CELL 



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

 on account of its very marked staining capacity when treated with 

 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 //;//// (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 micleoli, 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 plasmosomes (Figs. 5, 7, /?, 

 10), are of spherical form, and 

 by treatment with differential 

 stains such as haematoxylin and 

 eosin are found to consist typi- 

 cally of a central mass staining 

 like the cytoplasm, surrounded 

 by a shell which stains like 

 chromatin. Those of the other 

 form, the " net-knots " (Netz- 

 knoten), or karyosomes t are either 

 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 

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

 undoubtedly been confounded in some instances with a true nucleolus 

 or plasmosome. 1 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 



Fig. 10. Two nuclei from the crypts of 

 Lieberkiihn in the salamander. [HEIDENHAIN.] 



The character of the chromatin-m-twork 

 (basichromatiri) is accurately shown. The upper 

 nucleus contains three plasmosomes or true 

 nucleoli ; the lower, one. A few fine linin-threads 

 (oxychromatiri) are seen in the upper nucleus 

 running off from the chromatin-masses. The 

 clear spaces are occupied by the ground-sub- 

 stance. 



