For many years the banks themselves decided what reserve ratio constituted a safe proportion of currency to hold against their demand deposits.

Question:

1. In "hold against", is the verb "hold" still a transitive verb requiring an object? To me, HOLD is always a transitive verb and in this case, the object is "currency". Am I right?
2. What does "against" mean here? "Against" could mean "in contrast". But what does it link with here? Hold currency against demand deposits? Still need to pinpoint the exact meaning of "against"?

Thanks.