190 Macfarlaiic — 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 



