"A circuit performed by a capital and meant to be a periodical process, not an individual act, is called its turnover. The duration of this turnover is determined by the sum of its time of production and its time of circulation."

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Even the clearest localization of pain in one area may, in fact, be originating from a distant area .... The reference of pain implies the existence of convergence of inputs within the spinal cord. This leads to the necessary involvement in central neural circuits in the simplest of peripheral disorders. It also leads to the possibility that the basic disorder is entirely central.

— Patrick David Wall