It is managed by the partners; now these are generally rich men, are seldom able to grapple with great business of detail, and are not disposed to spend their whole lives and devote their entire minds to it if they were able.

A person with the accumulated wealth, the education and the social place of a great London banker would be a 'fool so to devote himself.

He would sacrifice a suitable and a pleasant life for an unpleasant and an unsuitable life.
But still the detail must be well done; and some one must be specially chosen to watch it and to preside over it, or it will not be well done.
Until now, or until lately, this difficulty has not been fully felt.

The detail of the business of a small private bank was moderate enough to be superintended effectually by the partners.

But, as has been said, the detail of banking--the proportion of detail to the size of the bank--is everywhere increasing.