The mid-cap stock index was rocked by Thomas Cook's profit warning. The travel operator lost more than a quarter of its market value after saying that its third quarter results will fall below expectations hurt by the unrest in the Arab countries and weak domestic demand. It was the worst performer on the FTSE 250. Shares of international leisure travel company TUI Travel followed on the heels of Thomas Cook, falling approximately 8%.Furthermore, oil outfit Premier Oil moved to assure the market about production targets saying it expects a sharp increase in production rate of around 60,000 barrels of oil equivalent per day by the end of the year, as its Asian development projects ramp up output but its comments regarding its North Sea and Froy field, Norway projects displeased investors. Meanwhile, the index was also hurt by growing fears of the Eurozone debt contagion spreading to other countries. However, the successful Italian bond auction soothed market jitters.FTSE 250 - RisersDixons Retail (DXNS) 15.80p +7.85%Daejan Holdings (DJAN) 2,851.00p +3.64%Kesa Electricals (KESA) 140.80p +3.30%Betfair Group (BET) 678.50p +2.80%Barratt Developments (BDEV) 109.00p +2.73%Premier Foods (PFD) 18.33p +2.63%Bwin.party Digital Entertainment (BPTY) 141.80p +2.01%Ocado Group (OCDO) 193.90p +2.00%Laird (LRD) 193.80p +2.00%Rentokil Initial (RTO) 92.70p +1.87%FTSE 250 - FallersThomas Cook Group (TCG) 87.00p -29.10%TUI Travel (TT.) 202.40p -8.50%Supergroup (SGP) 876.50p -5.24%Premier Oil (PMO) 413.40p -4.92%Aquarius Platinum Ltd. (AQP) 299.00p -4.07%JKX Oil & Gas (JKX) 254.00p -3.75%Jupiter Fund Management (JUP) 246.60p -3.67%Fidelity China Special Situations (FCSS) 99.20p -3.60%Yule Catto & Co (YULC) 234.30p -3.58%Centamin Egypt Ltd. (CEY) 122.10p -3.55%