3401
Rats treated for 11 days with morphine and withdrawn for 36 - 40 h showed differences in the development of tolerance : about half of the animals showed a rigidity after the test dose of morphine that was not significantly less than in the controls and were akinetic ( A group ) .
 morphine, rigidity, morphine, akinetic
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 morphine, rigidity, morphine, akinetic