94 Hypothesis of Structure of Germ Substance 
easily able to assume any new somatic character what- 
ever which may be imposed upon them. It makes no 
difference in the case of the still unspecialized cell, or 
even in that of the cell which is in the first stages of 
specialization, whether the somatizing stimulus is onto- 
genetic, proceeding by indirect ways from the central 
zone, or functional, induced by the environment. For 
the embryonic cell is in itself thoroughly plastic. Con- 
sequently the young soma would also be plastic if 
it were not continually influenced by the formative stimuli 
proceeding from the central zone of development. This 
influence though it is more feeble than the functional stim- 
ulus proceeding from the environment and consequently 
unable to resist it, has nevertheless the advantage of be- 
ing continuously in action, and so of gaining the ground 
lost, as soon as the action of the environment ceases. 
The cells of the adult soma are on the contrary less 
plastic, because they are already considerably specialized. 
But every modification which their limited plasticity per- 
mits in them remains, since the opposition of the central 
zone of development has already ceased. The adult 
organism is much less elastic. But in respect to the 
permanence of results it is more plastic than the young 
one. 
And, as already said, this is entirely confirmed not 
only by the most commonplace phenomena, but also by 
the most careful embryologic researches. In fact con- 
siderable changes of form, which would be destructive 
to an adult organism are, on the contrary, very well 
borne by the young. But attentive observation of these 
processes shows us also, as stated, that the younger the 
organism the greater is its elasticity, which tends, when 
the disturbing action has ceased, to restore it to its 
