A gentleman once told me that he rarely passed another in the street without wondering if he had not accosted him in an improper manner. He knew very well that he had not, but the more he dwelt upon the possibility, the more doubtful he became, until the impulse to settle the question became so strong that he would retrace his steps and inquire. He asked if _nux vomica_ would help this trouble! I told him he needed mental training. "I have tried that," he answered. "I keep saying to myself, 'I will not think of it,' but it is no use; my head becomes hot, my sight blurred, my thoughts confused, and the only relief I find is to settle the question." I tried to point out the direction in which he was tending, and told him he must remind himself that even if he had accosted another improperly, it was a trifling matter compared to the injury to himself of giving way to this compulsion; moreover, the impression he would make upon the other by going back would be even worse than that of having so accosted him; and, finally, he must dwell upon the _probability_ that he had not offended the man, instead of the _possibility_ that he had. Having pursued this line of thought, he must force himself to think of something else until the besetting impulse was obliterated. I suggested that if a baseball player should become incapacitated for the game, he would not lessen his disappointment by reiterating, "I will not think of baseball," but if he persistently turned his thoughts and his practice to billiards he might in time forget baseball. "I never played baseball," he replied, "and don't even know the rules." This represents an extreme case of "doubting folly" a case in which the victim could no longer concentrate his thoughts on the simplest proposition outside the narrow circle to which his doubts had restricted him. If we once allow ourselves to wonder whether we have turned off the water, enclosed the check, or mailed the letter, it is but a step to an uncomfortable frame of mind which can be relieved only by investigating the matter. This compulsion once acceded to, it becomes more and more easy to succumb. The next step is to blur, by constant repetition, the mental image of the act. In extreme cases the doubter, after turning the gas on and off a dozen times, is finally in doubt whether he can trust his own senses. A certain officer in a bank never succeeded in reaching home after closing hours without returning to try the door of the bank. Upon finding it locked, he would unlock it and disappear within, to open the vault, inspect the securities, and lock them up again. I once saw a victim of this form of doubt spend at least ten minutes in writing a check, and ten minutes more inspecting it, and, after all, he had spelled his own name wrong!