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 
