Graph showing the biphasic distribution of paw directed behaviour shown after an injection of 1% formalin into the hind paw of a rat

 

The time spent favouring, lifting and licking the injected paw increased to about 190 sec in the first five minutes and then decreased to about 20 seconds by 15 minutes after treatment. Times then rose gradually to reach a peak of about 250 sec between 30 and 40 minutes after treatment - decreasing to about 190 sec at 60 seconds after treatment.  (Maximum value possible is 300 seconds in any 5 minute period) (Abbott et al 1995).