The hardest hit of all that week were Walltreet's specialist firms ,the traders who were charged with maintaining orderly markets. That task required them to purchase stocks when there were no other buyers and to make sales when other sellers disappeared. Until the end of each had handled the shares of 20 to 30 specified Big Board companies. On Black Monday,the specialists grimly fulfilled their responsibilities,buying millions of shares as prices plunged all around them. Their losses could amount to as much as $ 750 million. Securities firms outside wall Street also felt mortal pain. The 4 500 accounts of the New York Stock Exchange member were taken over by Rodman & Renshaw,a Chicago firm.