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English philosopher John Stuart Mill experienced a several-months-long period of what he called " a dull state of nerves " , when one is " unsusceptible to enjoyment or pleasurable excitement ; one of those moods when what is pleasure at other times , becomes insipid or indifferent " .
 person: John Stuart Mill
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 person: John Stuart Mill