162 MUTATION 



unequal increase or decrease of these constituents, the 

 lower units. We speak of the simple growth of a cell 

 when its mass increases without any alteration in its 

 composition . . . but the cell changes its constitution 

 when this proportion is disturbed, when, for instance, 

 the red pigment granules which were formerly present 

 "but scarcely visible increase so that the cell looks red. If 

 there had previously been no red granules present, they 

 might have arisen through the breaking up of certain 

 particles — of protoplasm, for instance, — in the course 

 of metabolism so that, among other substances, red 

 granules of uric acid or some other red stuff were pro- 

 duced. In this case, also, the qualitative change would 

 depend on an increase or decrease of certain simpler 

 molecules and atoms constituting the protoplasm-mole- 

 cule. Thus, in ultimate instance, all variations depend 

 upon quantitative changes of the constituents of which 

 the varying part is composed." 



So far Weismann. With his accustomed thor- 

 oughness he has followed the consequences of his 

 stand that quantitative changes alone are suf- 

 ficient to account for the processes of evolution, 

 although to do so he has been forced to take the 

 position that the loss of certain atoms from a 

 moleclile is merely a quantitative change, and 

 that the appearance of a new quality is quantita- 

 tive because merely of the order of a change from 

 zero to one ! Weismann's argument here degen- 

 erates to a mere play of words. Just as good an 

 argument could be made to support the assertion 

 that all changes are qualitative — ^that 96 is qual- 

 itatively unlike 97. But if the ideas are both 

 to be retained, then it must be admitted that a 

 loss of atoms from a molecule, the appearance of 



