He took it out--looked at it with an expression of annoyance and surprise--and once more turned aside from the direct way to Lincoln's Inn Fields.
The envelope contained his last prescription.

Having occasion to consult the "Pharmacopoeia," he had written it at home, and had promised to send it to the patient immediately.

In the absorbing interest of making his preparations for leaving England, it had remained forgotten in his pocket for nearly two days.

The one means of setting this unlucky error right, without further delay, was to deliver his prescription himself, and to break through his own rules for the second time by attending to a case of illness--purely as an act of atonement.
The patient lived in a house nearly opposite to the British Museum.

In this northward direction he now set his face.
He made his apologies, and gave his advice--and, getting out again into the street, tried once more to shape his course for the College of Surgeons.