They talked for a long time of an operation, and did finally trephine, without result.

"The doctors say that they would suppose it was a fractured skull, or concussion of the brain, or something like that; but they've examined him and there is nothing to see on the outside; and they trephined and it didn't do any good; so they just let him stay about the hospital.

Fifteen months afterwards he was trephined at Greenwich Hospital, having been insensible all that time.

Suppose he had never been trephined, when would his intelligence have returned?