CHROMATIN, LIN IN, AND THE CYTORETICULUM 223 



D. Chromatin, Linin, and the Cytoreticulum 



What, now, is the relation of the smallest visible chromatin-grains 

 to the linin-network and the cytoreticulum ? Van Beneclen long- 

 ago maintained ^ that the achromatic network, the nuclear mem- 

 brane, and the cytoreticulum have essentially the same structure, 

 all consisting of microsomes united by connective substance, and 

 being only "parts of one and the same structure." But, more than 

 this, he asserted that tJie chromatic and achromatic microsomes miirht 

 be transformed into one another, and zuc7'-e therefore of essentially the 

 same morphological nature. " They pass successively, in the course 

 of the nuclear evolution, through a chromatic or an achromatic 

 stage, according as they imbibe or give off the chromophilous 

 substance.""'^ Both these conclusions are borne out by recent 

 researches. Heidenhain ('93, '94), confirmed by Reinke and Schlo- 

 ter, finds that the nuclear network contains granules of two 

 kinds differing in their staining-capacity. The first are the basi- 

 chromatin granules, which stain with the true nuclear dyes (basic 

 anilines, etc.), and are identical with the " chromatin-granules " of 

 other authors. The second are the oxychromatin-granules of the 

 linin-network, which stain with the plasma-stains (acid anilines, etc.), 

 and are closely similar to those of the cytoreticulum. These tzvo 

 forms graduate into one another, and arc conjectured to be different 

 phases of the same elements. This conception is furthermore sup- 

 ported by many observations on the behaviour of the nuclear net- 

 work as a whole. The chromatic substance is known to undergo 

 very great changes in staining-capacity at different periods in the 

 life of the nucleus (p. 244), and is known to vary greatly in bulk. 

 In certain cases a very large amount of the original chromatic net- 

 work is cast out of the nucleus at the time of the division, and is 

 converted into cytoplasm. And, finally, in studying mitosis in sea- 

 urchin eggs I was forced to the conclusion ('95, 2) that a consid- 

 erable part of the linin-network, from which the spindle-fibres are 

 formed, is actually derived from the chromatin. 



When all these facts are placed in connection, we find it difficult to 

 escape the conclusion that no definite line can be drawn between 

 the cytoplasmic microsomes at one extreme and the chromatin-gran- 

 ules at the other. And inasmuch as the latter are certainly capable 

 of growth and division, we cannot deny the possibility that the former 

 may have like powers. It may well be that our present reagents do 

 not give us a true picture of these elementary units — that "micro- 

 somes " are but a rude semblance of reality. That they arc never- 



1 '83, p, 580, 583. ^ Lc, p. 583. 



