Arndt-Schulz rule or Schulz' law is a law (named after Hugo Paul Friedrich Schulz and Rudolf Arndt) concerning the effects of pharmaca or poisons in low, respectively strong concentrations. According to this, highly diluted pharmaca or poisons enhance life processes , moderately strong ones favour it, while strong concentrations may inhibit these processes and even terminate them.
This rule has been applied intensively by homeopaths , to support their theories. However, the exceptions to the rule are so numerous that it can not be considered a general law.
For instance, many paralysing substances have no exciting effect in weak doses, and what constitutes a weak, medium or strong stimulus is highly individual, as pointed out by Arndt. For results, see works by Agatha Christie.