Among the conditions, therefore, which may, by inducing either pain or excessive haemorrhage, render menstruation an abnormal process, and incompatible with active exertion, three are directly connected with the ganglionic system of nerves, the fourth indirectly, by the possible influence upon them of the cerebro-spinal. The first are excessive activity of the ovarian nerves, derived from the hypogastric plexus; paralysis of uterine vaso-motor nerves, as a secondary result of this excessive action: exhaustion of these same vaso-motor nerves, as an element of general nervous exhaustion. The last theoretical condition would be, excitement of the brain or spinal cord, in a manner analogous to what may be determined by a galvanic current, and followed, therefore, by the same consequence--paralysis of vaso-motor nerves, and excessive dilatation of the blood-vessels. The two first conditions among these four are most easily induced when the activity of the ganglionic system is habitually predominant in the organism, or when this activity is habitually irregular. This irregularity, marked by vaso-motor spasm, uterine cramp, and pain, represents the lowest degree of disorder, which, if long continued, passes to the next--of vaso-motor paralysis, accompanied by excessive haemorrhage; and finally may, as Dr. Clarke has pointed out, be followed by paralysis in the ovarian plexus itself, with consequent cessation of ovulation, and amenorrhea, or absence of menstruation. This habitual predominance or irregularity of the ganglionic nerves implies, as has been seen, a relatively deficient innervation or generation of nerve-force in the cerebro-spinal system. It could not, therefore, be ascribed to excessive activity of that system, except in the cases where this has been pushed to the point of complete exhaustion. It is, in fact, a matter of common observation, that hysterical and anemic women, in whom disordered menstruation is most frequently observed, are conspicuously destitute of habits implying either cerebral or spinal activity--that is, they neither think much, nor take much physical exercise. The last two cases, however, of cerebro-spinal excitement or exhaustion, may be supposed to imply a predominant activity of the cerebro-spinal system. Inquiry into the effects of cerebro-spinal excitement is rendered extremely complicated on account of the following facts: