MYSTERY OF THE CELL 367 



chromatin) immediately breaks up, and Ixvomps scattered in the 

 form of minute granules in tlic delicate nuclear network, so that 

 finally a nucleus is formed of exactly the same structure as that 

 with which we started." 



Weismann then discusses and explains the meaning of this 

 strange phenomenon. He says: 



" It is evident, as Wilhelm Koux was the first to point out, that 

 the whole complex, but wonderfully exact, apparatus for the division 

 of the nucleus exists for the purpose of dividing the chromatin 

 substance in a fixed and regular manner, not merely quantitatively, 

 but also in i-espect of the different qualities which must be contained 

 in it. So complicated an apparatus wouhl have been unnecessary 

 for the quantitative division only. W, however, the chromatin sub- 

 stance is not uniform, but is made up of several or many different 

 qualities, each of which has to be divided as nearly as possible into 

 halves, or according to some definite rule, a better apparatus could 

 not be devised for the purpose. On the strength of this argument 

 we may, therefore, represent the hereditary substance as consisting 

 of different qualities. . . . The statement that this substance 

 is the hereditary substance can, therefore, hardly be considered as 

 an hypothesis any longer." ^ 



After some further discussion of the views of other writers, 

 he goes on to show that the chromatin substance is not only 

 contained in the germ-cells, but also in all the cells of the 

 entire organism in each phase of its development, which is 

 effected bv the constant division of the cells and their nuclei, 

 the chromatin continuing to grow during the whole time. But 

 in the body it enters on a long and complex process of growth, 

 so as to build up the substance of all the varied organs and 

 tissues, and also for the repair or renovation of these various 

 tissues as they require it. He illustrates the successive 

 changes which he supposes the chromatin to bring about, and 

 for which purpose it is so accurately divided and subdivided 

 from the very beginning, in the following inissage: 



1 The Gcnn-Plasm, p. 29. 



