18 



THE AMERICAN NATURALIST 



[Vou L 



it occurs. Methyl-green has been claimed to be the most 

 reliable and certain of nuclear stains, but R. Hertwig, in 

 his classical researches upon ActinosplKcrium, showed 

 that it sometimes fails to stain chromatin. It is perfectly 

 conceivable that there might be varieties of chromatin 

 which could not be stained by any dye whatsoever. 



I have felt bound to insist strongly upon the inadequacy 

 of staining-methods for the detection and identification 

 of chromatin, well known though these facts are to every 

 cytologist, because here also I note a tendency amongst 

 biological chemists to regard staining-properties as the 

 sole criterion of chromatin. In reality such properties 

 are of entirely secondary importance. To use the ter- 

 minology of formal logic, staining-properties are an 1 1 ac- 

 cident," though it may be an "inseparable accident/' of 

 chromatin, not a "difference" which can be used to frame 

 a logical definition, per genus et differentias, of this sub- 

 stance. If chromatin were nothing more than ' ' stainable 

 substance," as Professor Armstrong terms it, 9 some of 

 the most important results of cytological investigation 

 would be deprived of all real significance and reduced to 

 the merest futilities. 



What then is the true criterion of the chromatin-sub- 

 stance of living organisms f From the chemical point of 

 view the essential substance of the cell-nucleus would ap- 

 pear to be characterized by a complexity of molecular 

 structure far exceeding that of any other proteins, as 

 well as by certain definite peculiarities. Especially char- 

 acteristic of chromatin is its richness in phosphorus-com- 

 pounds, and it stands apart also from other cell-elements 

 in its solvent reactions, for example, resistance to peptic 

 digestion. E. B. Wilson, in his well-known treatise, has 

 emphasized the ' ' cardinal fact . . . that there is a definite 

 and constant contrast between nucleus and cytoplasm." 

 The outstanding feature of the nucleus is the constant 

 presence in abundance of nuclein and nucleoproteins. 

 Nuclein, which is probably identical with chromatin, is a 



9 Science Progress, Vol. VII, p. 327. 



