Look at it in this light.

On what occasion would it be most probable that such a presentation would be made?
When would his friends unite to give him a pledge of their good will?
Obviously at the moment when Dr.Mortimer withdrew from the service of the hospital in order to start in practice for himself.

We know there has been a presentation.

We believe there has been a change from a town hospital to a country practice.

Is it, then, stretching our inference too far to say that the presentation was on the occasion of the change ?" "It certainly seems probable." "Now, you will observe that he could not have been on the staff of the hospital, since only a man well-established in a London practice could hold such a position, and such a one would not drift into the country.