n] THE NUCLEUS 17 



cytoplasmic over nuclear volume has been removed. It 

 seems, therefore, that although the law of the constant ratio 

 between nuclear and cytoplasmic volume is by no means 

 universal, this ratio has considerable importance in the life 

 of the cell, and is perhaps one of the factors which brings 

 about cell-division. 



A typical nucleus consists of a closed membrane enclosing 

 a more or less obvious network of threads, the meshes of 

 which are occupied by a fluid. Observations such as those 

 of HARDY have thrown some doubt on the existence of the 

 network in the nucleus of the living cell, but in some cases 

 at least a real network has been described as visible in 

 living nuclei, and other reasons will be given later for be- 

 lieving that a true structure exists in life. The network is 

 usually described as consisting of a substance called linin, 

 which stains with acid stains ; while along the strands, and 

 especially at the nodes of the meshes, there are more or less 

 conspicuous granules of the substance known as chromatin, 

 from the fact that it stains more easily and deeply than the 

 other constituents of the nucleus (Greek chroma, colour). 

 It is from the chromatin that the bodies called chromosomes, 

 which play a great part in nuclear division, are formed. With 

 regard to the word linin there is a difference of usage among 

 different observers. Some use the term for the oxyphil sub- 

 stance of which the threads of the network seem to be 

 chiefly composed, but others maintain that this substance 

 really consists of oxyphil granules embedded in a non- 

 staining ground-work, and that it is to the latter that the 

 term linin should properly be applied. HARDY found that it 

 was possible to fix nuclei in such a way that no network 

 appeared, but merely an assemblage of granules, some of 

 which took basic and others acid stains ; of these the basiphil 

 granules are doubtless chromatin and the oxyphil probably 

 D. c. 2 



