CHAP, v.] OF REGENERATION. 337 



according to M. Ranvier it regenerates itself by traversing all the 

 phases through which it has already passed from the beginning 

 of its foetal development. The nervous centres, the central 

 hemispheres even, seem to be able to restore themselves in a 

 certain degree. How otherwise explain a large number of incon- 

 testable cases of complete re-establishment of the intellectual 

 faculties after serious lesions, and even after notable losses of 

 substance of the encephalon ? 



No doubt, the biological facts, like all the phenomena of the 

 universe, obey laws, true laws, inflexible, and without exception. 

 But those facts are so complex, so intermingled, the ensemble of 

 their causes forms a skein so entangled, that the most of our 

 pretended biological laws are simply imperfect generalisations, 

 suffering many exceptions and always subject to revision. 



