182 CHEMICAL NATURE OF THE NUCLEUS. 



substance. The chromatin is sometimes in the form of fine particles, which are 

 arranged in a linear manner to form filaments. 



The term chromatin was originally employed by Flemming to denote the whole substance 

 of the chromoplasmic filaments, but since it has been shown (by Carnoy and others) that those 

 filaments are actually composed of two substances, one stainable and the other remaining 

 unstained by most dyes, it is advisable to restrict the use of the term in the manner above 

 indicated. The particulate structure of nuclear filaments was first noticed by Pfitzner in the 

 V-shaped loops of certain dividing nuclei. 



As to the membrane bounding the nucleus, this has been regarded by most 

 authors as a distinct wall shutting it off from the protoplasm of the cell. Others look 



Fig. 210. PART OF THE NUCLEAR FILAMENT OF THE CELL SHOWN IN FIG. 208. 

 GREATLY MAGNIFIED. (Carnoy.) 



upon it as being merely a dense superficial portion of the chro- 

 moplasmic network, and therefore as not complete, but rather 

 of the nature of a basket-work permitting of intercommunica- 

 tion between the cell -hyaloplasm and the nuclear matrix. Others, 

 who admit the incompleteness of this chromoplasmic membrane, 

 yet describe a complete enclosing membrane of achromatic 

 substance separating the nucleus from the cell-protoplasm. 

 Chemical nature of the . nucleus. Not much is known regarding the 

 chemical nature of the cell nucleus. Miescher described in the nuclei of pus 

 cells a substance to which he gave the name nuclein, which is characterised by the 

 resistance which it offers to most chemical reagents, especially to acids and 

 digestive juices, and by its containing a considerable quantity of phosphorus. 

 This substance is in all probability identical with Flemming's chromatin. The 

 achromatic material of the chromoplasmic fibres, which has received the name 

 of linin, has been conjectured to be similar to the plastin which is found in cell- 

 protoplasm. The composition of the nuclear matrix and of the spindle of achromatic 

 fibrils which makes its appearance in the nucleus during karyokinesis is completely 

 unknown, but the fibres of the spindle are probably composed of linin. 



The nucleus has been supposed by some histologists to be identical in nature 

 with protoplasm. Its behaviour, however, with many reagents is altogether different ; 

 and in general it may be said that it offers greater resistance to their action than the 

 substance which surrounds it. Moreover, its chromoplasm stains much more 

 intensely with haematoxylin and many other reagents, than does protoplasm, and, on 

 the other hand, it remains in some cases unstained by reagents which colour protoplasm 

 intensely, for example, solution of chloride of gold. So that chemically at least there 

 is a considerable difference between the nucleus and the protoplasm. But if we 

 regard the spontaneous changes which are manifested by both, and especially the 

 important part which the nucleus plays in the division of the cell, as will be imme- 

 diately described, there is much in favour of the view which regards the nucleus as 

 a portion of the living substance somewhat altered in chemical nature, which is set 

 aside to preside over the reproduction of the cell, and perhaps also over other 

 functions. In favour of this view there are observations which show that under certain 

 circumstances, the nucleus may enlarge at the expense of the protoplasm, even to the 

 extent of absorbing the greater part of the latter, so that the whole cell is little else 

 than nucleus ; indeed, this relative increase of size of the nucleus seems to be a 

 change which constantly precedes the phenomena of cell-division. 



Functions of the nucleus. Various observers have described in the cells of 

 secreting glands and elsewhere, a spherical body which is either partly attached to 

 the nucleus or is at least closely connected with it. This has been spoken of 

 as the paranucleus (German, Nebenkerri), and it is described as having been 



