{HEAD ~ The guinea pigs} are housed under standard laboratory conditions on a 7 a.m. to {TAIL ~ 7 p.m. lighting schedule} for at least seven days prior to experimentation 
{ HEAD ~ The guinea pigs } are housed under standard laboratory conditions on a 7 a.m. to { TAIL ~ 7 p.m. lighting schedule } for at least seven days prior to experimentation
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH