MORPHOLOGY 33 



and the second, nucleolus or plasmosome. Absolute distinction 

 between these two terms cannot be made as they are based upon 

 the difference in affinity to nuclear stains which cannot be stand- 

 ardized and hence do not give uniformly the same result. Fol- 

 lowing Minchin and others, the term endosome is advocated here 

 to designate one or more conspicuous bodies other than the 

 chromatin granules, present within the nuclear membrane. 



When viewed in life, the nucleoplasm is ordinarily homo- 

 geneous and structureless. But, upon fixation, there appear in- 

 variably plastin strands or networks which seem to connect the 



Nuclear membrane 

 Endosome 

 Achromatic strand 

 Chromatin granules 

 a b 



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



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 be- 

 come 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 Barbu- 

 lanympha (Fig. 131, c), according to Cleveland and his associates 

 (1934). Others maintain that the achromatic structures promi- 

 nent in fixed vesicular nuclei are mere artifacts brought about 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 

 substances remain unattacked; and 4) in the fixed condition 



