190 Macfarlane—Current Problems 
disposed along a rather less deeply-stained ribbon, the linin. 
As the prophase advances toward the metaphase stage, split- 
ting of these granules occurs, as described carefully by the 
above author. Later, the longitudinal splitting of the ribbon 
along which these are disposed, gives rise to the daughter 
chromosomes. 
The main point of discussion at the present time is as to the 
possible value of the three constituents just described. The 
nucleoplasm does not seem to differ fundamentally from the 
general cytoplasm. The nuclear framework, however, pre- 
sents greater difficulties. During the past ten years or more, 
this has generally been regarded as composed of linin and 
chromatin constituents intimately related, the latter as the 
bearer of hereditary substance, the former as the framework 
for distribution of the hereditary substance. Great emphasis 
has been laid on relative stainability of these and of the 
nucleolus by acid and basic stains. But the past two years 
has witnessed a decided change of opinion by many authors. 
Fischer’s recent definition of chromatin is: “ The nucleic acid 
containing stainable substance of the cell nucleus, which with 
increasing content of nucleic acid always stains less strongly 
with acid watery stains.” 
Such a definition does not preclude the presence of sub- 
stances which may be related to nucleic acid on the one hand, 
and to albumens on the other. It seems, in fact, as if the 
fundamental mistake of the past fifteen years has been in 
accepting that the highest phosphorus-containing portion of 
the nucleus, viz., chromatin, is the most important material as 
hereditary substance, and that all else was accessory to it. 
The nucleolus, as well as parts of the nucleus, consist of 
complex albuminous compounds. The linin substance stains 
deeply with many protoplasmic stains, and is large in amount. 
Undue emphasis we believe has been given to the chromatin 
granules as the sole bearers of heredity. Since linin and 
