Arndt's law

[ärnts]
n.
  1. The principle stating that weak stimuli excite physiological activity, moderately strong stimuli favor it, strong stimuli retard it, and very strong stimuli arrest it.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.