THE CHEMISTRY AND PHYSICS OF THE CELL 53 

 THE NUCLEUS 1 



Although the nucleus presents morphologically a sharp iso- 

 lation from the cytoplasm, and displays equally sharp tinctorial 

 differences, it is probable that chemically the differences be- 

 tween nucleus and cytoplasm are quantitative rather than quali- 

 tative. The characteristic affinity of certain elements of the 

 nucleus for basic stains depends upon the presence in the 

 nucleus of nucleoproteids in large proportion, and to a lim- 

 ited degree nucleoproteids are characteristic of nuclei. Their 

 affinity for basic dyes depends upon their acidity, which is due 

 to the nucleic acid radicle. In inverse proportion to the degree 

 to which this acidity is neutralized by proteid groups in the 

 nucleo-proteid molecule, the nucleo-proteid will show affinity for 

 basic dyes. For example, the heads of spermatozoa contain 

 nucleic acid bound to little or no proteid, hence they are 

 very acid, have a corresponding affinity 'for basic dyes, and 

 appear intensely stained by hematoxylin, etc. Ordinary 

 chromatin threads of nuclei appear to contain somewhat 

 more proteid in their nucleoproteid molecules, and hence 

 stain less intensely than do the spermatozoa heads, except 

 when in karyokinesis, when the chromatin nucleoproteid 

 seems to approach that of the spermatozoa in acidity. We 

 also have nucleoproteids with the nucleic acid so thoroughly 

 saturated by proteid that they do not stain at all by basic dyes, 

 and these seem to exist principally in the cytoplasm, and also 

 to form the ground-substance of the nuclei, occupying the spaces 

 between the chromatin particles (this achromatic substance of 

 the nuclei is called linin or plastin by some cytologists). Besides 

 the chromatin and the nucleoli, there is a peculiar chromatophile 

 substance, suspended in the finer part of the nuclear structure 

 in the same manner as the chromatin itself is in the coarser 

 portions ; this was called lanthanin by Heidenhain, 2 and is prob- 

 ably similar to the substances also described as parachromatin 

 and paralinin. Undoubtedly the other forms of proteids found 

 in the cell, such as globulin, albumin, and nucleoalbumin, exist 

 both in the nucleoplasm and in the cytoplasm, the essential dif- 

 ference being that the proportion of nucleoproteid is much 

 greater in the nucleus, and that the nucleoproteids of the cyto- 

 plasm contain relatively more proteid in proportion to the 

 nucleic acid than do the nucleoproteids of the nucleus. As 

 nucleoproteids are little affected by peptic digestion, it is possible 



1 Earlier literature by Albrecht, " Pathologic der Zelle, " Lubarsch-Oster- 

 tag Ergeb. der allg. Pathol., 1899 (6), 900. 



2 Festschr. f. Kolliker, 1892, p. 128. 



