4th. An impression made on one part of the sympathetic system is easily communicated to another, and to the ganglionic masses of the visceral plexuses, already described. Hence the rapid effect of many emotions upon the processes of digestion; hence the epigastric response to the emotion of fear, which led Bichat to localize this feeling in the solar plexus lying behind the stomach. In a precisely similar manner may the effect of emotion be distributed to the ganglionic nerves of the kidneys, uterus, and ovaries, leading to the flow of urine that terminates a paroxysm of hysteria, often suppressing menstruation, by contraction of uterine blood vessels, or causing an excess of menstrual haemorrhage, from an excessive excitement of the ovarian nerves during the menstrual crisis. None of these effects are observed after a simple act of thinking, unattended by emotion. 5th. Probably on account of such an influence upon the vaso-motor nerves, the blood vessels, and, consequently, the processes of nutrition, the evolution of emotions is attended with much greater fatigue than is that of thought. The fatigue that may follow a prolonged intellectual operation is, moreover, distinctly localized in the head, and exists in various degrees, from simple inability for further attention, to decided sensation of weariness, or even pain. But the fatigue experienced after excessive emotion, especially if this be of a depressing character and accompanied by tears (which imply vaso-motor paralysis in the lachrymal glands), is generalized all over the body, and is, moreover, very much more often followed by headache, or by symptoms of cerebral congestion or anemia, than is the act of thinking, except in persons morbidly predisposed. When nervous exhaustion is observed after prolonged mental effort, one of two other conditions, or both, has nearly always co-existed, namely, deficiency of physical exercise, or presence of active emotion, as, ardent ambitions or harassing anxieties. In a few cases, the mental effort itself, by the afflux of blood determined to the brain, or the excessive activity imposed upon its elements, becomes an efficient cause of disease. But in these cases there is either an original imperfection in the organization of the nerve tissues, or the mental effort has been of that exceptionally intense nature of which none but a few minds are capable. Finally, in these cases, the resulting disease is seated in the brain or spinal column. This latter remark is of great importance for our purpose; for it tends to show that diseases produced elsewhere within the range of the ganglionic system of nerves--as the menstrual haemorrhage, that we are especially considering--must be due to some other nervous act than that of thought.