When Fisher Scientific International agreed to buy PSS World Medical Inc. in an all-stock deal valued at roughly $840 million at the time of the announcement, PSS shareholders should have been content. After all, their company's stock was hovering at near-record lows in the wake of a disastrous year for PSS. But shareholders were cool, partly because they were unhappy with PSS' quarterly earnings report, announced the same day, partly because they didn't know Fisher, and partly because they were caught up in a web of arbitrage, which drove down the stocks of both companies 25%.Fisher, an international distributor of scientific supplies, sees PSS as a way to expand its customer and vendor bases and to take advantage of cross-channel opportunities. The companies don't have much product overlap, with PSS strong in alternate site markets and Fisher a force in research labs and acute care hospitals. Fisher is relatively unknown on Wall Street, because only 7% of its shares are publicly traded. And PSS, while reeling from a series of problems, has a healthy underlying business as the market leader in alternate site markets for hospital and lab supplies. Now, Fisher and PSS have to convince Wall Street that they mean business.