Conditions Necessary for Inheritance 287 



to specific alterations of a single form of energy, so that 

 the latter appears, as it were, the common denominator 

 for these variations that are quite unlike in nature and 

 whose combination or separation is thus permitted as 

 often as required. 



2. The determinative influence which the germ sub- 

 stance in its totality exerts upon the soma cannot be 

 limited to the first moment of the first cleavage of the 

 egg but must persist throughout the whole of ontogeny 

 up to the adult condition, so that the germinal substance 

 never as it were loses touch with the soma, but rather 

 remains in a continual state of reciprocal action and 

 reaction with it. 



3. The influence exerted by the soma in this way 

 must be reversible, that is the germ substance must be 

 influenced in such a way that it can call forth again at the 

 proper moment, at the numberless different points of the 

 soma of the new organism, all the same, respective, 

 special, somatic conditions by whose complex modes of 

 being the germ substance itself was already influenced in 

 the parent organism in so special a way. 



This last condition which alone implies in itself the 

 whole question of inheritance falls again into two parts. 

 First the germ substance must be influenced always in 

 such a way that it is capable of giving back at the required 

 moment the same influence, qualitatively identical but in 

 the reverse direction, which it had already experienced 

 as the single resultant of all the elementary somatic in- 

 fluences to which this germinal substance was simulta- 

 neously subjected in the preceding organism. Second: 

 the germ substance which thus gives back again the 

 influence, by which it was influenced, qualitatively 

 identical but in reverse direction, must be localized at a 



