MORPHOLOGY 35 



When viewed in life, the nucleoplasm is ordinarily homogeneous 

 and structureless. But, upon fixation, there appear invariably plastin 

 strands or networks which seem to connect the endosome and the 

 nuclear membrane. Some investigators hold that these strands or 

 networks exist naturally in life, but due to the similarity of refractive 

 indices of the strands and of the nucleoplasm, they are not visible 

 and that, when fixed, they become readily recognizable because of a 

 change in these indices. In some nuclei, however, certain strands 

 have been observed in life, as for example in the nucleus of the 

 species of Barbulanympha (Fig. 152, c), according to Cleveland and 

 his associates (1934). Others maintain that the achromatic structures 

 prominent in fixed vesicular nuclei are mere artifacts brought about 



Nuclear membrane 

 Endosome 

 Achromatic strand 

 Chromatin granules 

 a b 



Fig. 2. a, vesicular nucleus; b, compact nucleus (diagrams). 



by fixation and do not exist in life and that the nucleoplasm is a 

 homogeneous liquid matrix of the nucleus. 



The chromatin substance is ordinarily present as small granules 

 although at times they may be in block forms. Precise knowledge 

 of chromatin is still lacking. At present the determination of the 

 chromatin depends upon the following tests: (1) artificial digestion 

 which does not destroy this substance, while non-chromatinic 

 parts of the nucleus are completely dissolved; (2) acidified methyl 

 green which stains the chromatin bright green; (3) 10 per cent 

 sodium chloride solution which dissolves, or causes swelling of, 

 chromatin granules, while nuclear membrane and achromatic sub- 

 stances remain unattacked; and (4) in the fixed condition Feulgen's 

 nucleal reaction. The vesicular nucleus is most commonly present 

 in various orders of the Sarcodina and Mastigophora. 



The compact nucleus (Fig. 2, b), on the other hand, contains a 

 large amount of chromatin substance and a comparatively small 

 amount of nucleoplasm, and is thus massive. The macronucleus of 

 the Cihophora is almost always of this kind. The variety of forms 

 of the compact nuclei is indeed remarkable. It may be spherical, 

 ovate, cylindrical, club-shaped, band-form, moniliform, horseshoe- 

 form, filamentous, or dendritic. The nuclear membrane is always 



