Very much of it is repayable at demand, or at very short notice.

The demands on a broker in periods of alarm may consequently be very great, and in practice they often, are so.

In times of panic there is always a very heavy call, if not a run upon them; and in consequence of the essential nature of their business, they cannot constantly keep a large unemployed reserve of their own in actual cash, they are obliged to ask help of some one who possesses that cash.

By the conditions of his trade, the bill-broker is forced to belong to a class of 'dependent money-dealers,' as we may term them, that is, of dealers who do not keep their own reserve, and must, therefore, at every crisis of great difficulty revert to others.
In a natural state of banking, that in which all the principal banks kept their own reserve, this demand of the bill-brokers and other dependent dealers would be one of the principal calls on that reserve.

At every period of incipient panic the holders of it would perceive that it was of great importance to themselves to support these dependent dealers.