HABIT A MODIFICATION OF BRAIN TISSUE.--But the nervous tissue is the most sensitive and easily molded of all bodily tissues. In fact, it is probable that the real _habit_ of our characteristic walk, gesture, or speech resides in the brain, rather than in the muscles which it controls. So delicate is the organization of the brain structure and so unstable its molecules, that even the perfume of the flower, which assails the nose of a child, the song of a bird, which strikes his ear, or the fleeting dream, which lingers but for a second in his sleep, has so modified his brain that it will never again be as if these things had not been experienced. Every sensory current which runs in from the outside world; every motor current which runs out to command a muscle; every thought that we think, has so modified the nerve structure through which it acts, that a tendency remains for a like act to be repeated. Our brain and nervous system is daily being molded into fixed habits of acting by our thoughts and deeds, and thus becomes the automatic register of all we do. The old Chinese fairy story hits upon a fundamental and vital truth. These celestials tell their children that each child is accompanied by day and by night, every moment of his life, by an invisible fairy, who is provided with a pencil and tablet. It is the duty of this fairy to put down every deed of the child, both good and evil, in an indelible record which will one day rise as a witness against him. So it is in very truth with our brains. The wrong act may have been performed in secret, no living being may ever know that we performed it, and a merciful Providence may forgive it; but the inexorable monitor of our deeds was all the time beside us writing the record, and the history of that act is inscribed forever in the tissues of our brain. It may be repented of bitterly in sackcloth and ashes and be discontinued, but its effects can never be quite effaced; they will remain with us a handicap till our dying day, and in some critical moment in a great emergency we shall be in danger of defeat from that long past and forgotten act. WE MUST FORM HABITS.--We _must_, then, form habits. It is not at all in our power to say whether we will form habits or not; for, once started, they go on forming themselves by day and night, steadily and relentlessly. Habit is, therefore, one of the great factors to be reckoned with in our lives, and the question becomes not, Shall we form habits? but _What habits we shall form._ And we have the determining of this question largely in our own power, for habits do not just happen, nor do they come to us ready made. We ourselves make them from day to day through the acts we perform, and in so far as we have control over our acts, in that far we can determine our habits. 2. THE PLACE OF HABIT IN THE ECONOMY OF OUR LIVES