Nowhere but on Wall Street does the phrase "One man's trash is another man's treasure" ring so true. And perhaps no one knows that better than Mack the Knife.

Morgan Stanley's John Mack, who saved about $1 billion by firing 4,800 people so far this year, is gingerly spending the savings on new hires, according to a report in the Financial Times. It's already spent $400 million on new recruits, and it hopes to spend the remaining $600 million by the end of this year.

The bank sent pink slips to about 10 percent of its workforce in January and April, mostly in areas like investment banking, research, and fixed income. It plans to hire new staff in areas such as derivatives, risk management, and proprietary trading.

Mack told associates that the massive financial layoffs across the Street have presented a historic opportunity to seize new talent. Banks are already trying to position themselves for the end of the credit crisis.

And Mack is starting with an unlikely new name: Morgan Stanley announced it has hired Luc Francois as head of European equities and global head of equity derivatives.

Francois was most recently employed by Société Générale, where he oversaw the equities unit when one of the bank's low-level traders, Jerome Kerviel, lost about $7.6 billion in bad trades. Francois left the bank after the scandal erupted, but he has not been named in any of the subsequent investigations into the matter.

Other new hires include former Bear Stearns executives Thomas Wong and Eric Cole in the proprietary trading unit.

The news underscores the ever-evolving ebb and flow of moneymaking businesses on Wall Street. Investment banks have a long history of beefing up certain desks to respond to the nature of the markets, only to be forced to shrink them in favor of other desks as the business changes.

It makes it particularly difficult for newly minted M.B.A. grads to choose their focus.