6 INTKODUCTIOX PEOTOPLASM THE CELL 



and often accumulate in knot-like groups to form the karyosomes, 

 the larger of which closely simulate the plasmosomes, or true 

 nucleoli. The chromatin granules are also prone to collect be- 

 neath the nuclear membrane, to the inner surface of which they 

 adhere. 



Chromatin possesses a strong affinity for basic dyes.* Its gran- 

 ules and threads are often so closely packed as to give to the 

 nucleus the appearance of a solid basophile mass. This condition, 

 however, is only found in the resting nucleus; in those nuclei 

 which are undergoing mitotic changes the chromatin granules are 

 less abundant, less closely packed, and the achromatic portions 

 form a proportionately larger part of the nucleus. 



The nucleolus closely resembles the chromatin in its staining 

 properties. It forms a small spherical but solid basophile mass. 

 The nucleolus is described as a plasmosome, to distinguish it from 

 its simulacra, the larger karyosomes. The nucleolus entirely dis- 

 appears during cell division. 



The nuclear wall is likewise only found during the resting 

 stage of the cell as regards the phenomena of karyokinesis. It 

 closely resembles the chromatin, and, though somewhat variable 

 in its staining properties, is, as a rule, strongly basophile. It is 

 said to be composed of amphipyrenin (Schwarz f ). 



Cell Growth, Development, and Differentiation. The germ cell 

 is not only capable of reproducing itself by karyokinesis, but, in 

 the multicellular animals, is also capable of forming the tissue 

 cells which are so specialized or differentiated as to be no longer 

 capable, like the germ cell, of reproducing the animal species, but 

 which may produce other similar cells to form the various tissues 

 of the body. 



In such tissue cells there occur many modifications of the 

 typical cell structure. The exoplasm may be arranged as fibrillae 

 to form cilia, flagella, intercellular bridges, etc. The shape of the 

 cell may also be altered from its typical contour to a squamous, 

 columnar, polyhedral, fusiform, or even a stellate form, and the 

 cell may be subject to great variations in size. 



The endoplasm likewise presents great variations in structure. 



* Heidenhain describes the basophile chromatin as basichromatin, in contra- 

 distinction to the slightly acidophile properties of the exceedingly fine granules 

 which he demonstrated as forming the linin threads, and which he described as 

 oxychromaiin or lanthanin. 



f Breslau, 1887. 





