The same is true to even a larger extent of the emotional nature. Persons, in certain states of the nervous system, are pleased with persons, objects, and sensations, which afford them no pleasure at other times; they are displeased and pained, while in other conditions, with sentiments which would at other times produce no such effect. They sometimes feel that the world and its possessions and pleasures are so great and grand that they can never leave them, and the thought of doing so causes the keenest anguish; while in another state all these pleasures and possessions appear as empty and valueless as a bubble of air, and the thought of leaving them, and throwing off the burdens and cares of life, which are usually so much enjoyed, seems almost pleasurable. Again, some persons have periods of being irritable, restless, nervous; they cannot bear much; little incidents which, in other conditions of the nervous system, they would think little or nothing of, turn them into a passion of excitement, which can hardly be controlled for the time being. In other states they may long to weep, or to be in solitude where they cannot be disturbed; or they may shout, and laugh, and talk, while thoughts come coursing through the brain so fast that words fail in their expression. The same changes occur among the impulses; these are at times almost irresistible. Nearly every one, while standing on a high cliff or house-top, has felt an impulse to jump off or push his friend off, reckless of the consequences. In the usual condition of the nervous system persons love their children and relatives, and are ready to do and suffer and at times even to die for them, if need be, while at other times all these sentiments fade away, so that they are unconscious of them, and even the opposite sentiment of dislike or hatred takes their place. Periods of mental lethargy come over many persons at times, so that they care neither to talk nor engage in any of their usual intellectual or physical pursuits; and such stimuli as are usually sufficient to rouse the brain into action appear to have very little effect. They feel and say that there is a state of only partial brain-activity. At other times the brain acts with the greatest freedom; occurrences which took place long years before, and which, perhaps, have not been thought of since, come back with all the freshness of yesterday. Thoughts come rapidly. Keen flashes of wit, bright scintillations of thought, forms of expression of unusual felicity, pour forth spontaneously, while the mind apprehends and retains many kinds of knowledge with the greatest readiness. Similar variations take place in reference to courage and its opposite, timidity; truthfulness and suspicion; and, in fact, the whole range of mental endowments.