Describing the multi-bank liquidity injection, Paul Krugman writes:

...the Fed can come to the rescue. If the rumor is false, the bank has enough assets to cover its debts; all it lacks is liquidity — the ability to raise cash on short notice. And the Fed can solve that problem by giving the bank a temporary loan, tiding it over until things calm down.
Matters are very different, however, if the rumor is true: the bank really did make a big bad loan. Then the problem isn’t how to restore confidence; it’s how to deal with the fact that the bank is really, truly insolvent, that is, busted...What’s going on in the markets isn’t an irrational panic. It’s a wholly rational panic, because there’s a lot of bad debt out there, and you don’t know how much of that bad debt is held by the guy who wants to borrow your money...