That agent, force, or action in nature by the operation of which upon the organs of sight, objects are rendered visible or luminous.
"...once development was ended, the founts of growth and regeneration
of the axons and dendrites dried up irrevocably. In adult centres the
nerve paths are something fixed, ended, immutable. Everything may die,
nothing may be regenerated. It is for the science of the future to
change, if possible, this harsh decree."
- Santiago Ramon y Cajal
Degeneration and regeneration of the nervous system
"Nature does not know extinction; all it knows is transformation.
Everything science has taught me, and continues to teach me,
strengthens my belief in the continuity of our spiritual existence
- Wernher von Braun
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