The only securities which a banker, using money that he may be asked at short notice to repay, ought to touch, are those which are easily saleable and easily intelligible.

If there is a difficulty or a doubt, the security should be declined.

No business can of course be quite reduced to fixed rules.

There must be occasional cases which no pre-conceived theory can define.

But banking comes as near to fixed rules certainly as any existing business, perhaps as any possible business.