possible. But a doctor is not a detective; he should not go out of his way to assume police functions. He should keep his eyes and ears open, and, though, in general, he should keep his own counsel, it is his duty to note very carefully anything that seems to him likely to bear on any important legal issues. It is not his business officiously to initiate criminal inquiries, but it is emphatically his business to be ready, if called upon, to assist justice with information that his special knowledge and opportunities have rendered accessible to him. You see the bearing of this?"
"You mean that I should note down what I have seen and heard and say nothing about it until I am asked."
"Yes; if nothing further happens. But if you should be sent for again, I think it is your duty to make further observations with a view, if necessary, to informing the police. It may be, for instance, of vital importance to identify the house, and it is your duty to secure the means of doing so."
"But, my dear Thorndyke," I expostulated, "I have told you how I was conveyed to the house. Now, will you kindly explain to me how a man, boxed up in a pitch-dark carriage, is going to identify any place to which he may be carried?"
"The problem doesn't appear to me to present any serious difficulties," he replied.
"Doesn't it?" said I. "To me it looks like a pretty solid impossibility. But what do you sug-
