Or the opposite event may occur. As the stimulation of the vaso-motor nerves causes contraction of the blood-vessels, so their exhaustion or paralysis causes relaxation of these same vessels, consequently, over-distension with blood; and, if the door to hæmorrhage be once opened by the existence of the menstrual nisus, an excessive flow of blood.[39] Such vaso-motor paralysis may depend on one of three circumstances:
1st. The original stimulus may be excessive, and hence necessarily followed by reaction.
2nd. Schiff has shown that galvanization of a cerebro-spinal nerve causes a dilatation of the blood-vessels in the vicinity, as if the vaso-motor force were overpowered by the excessive stimulation of the controlling nerves. If excessive action of the brain or spinal cord be analogous in its effects to galvanism of a spinal nerve, it might be supposed to cause vaso-motor paralysis and hæmorrhage.
3d. In general exhaustion of the nervous system, both of its ganglionic and cerebro-spinal apparatus, the vaso-motor nerves suffer with the rest, and the blood-vessels lose their tone in consequence. It is to such exhaustion that Dr. Clarke especially attributes excessive uterine hæmorrhage in young girls, and, as already said, he refers the exhaustion to a single cause, namely, to the attempt to impose on the nervous system two actions of equal intensity, contrary to the fundamental law that an intense evolution of nerve-force in one part of the organism necessitates repose in the remainder.
Independently of the three conditions where excessive menstruation is connected with vaso-motor paralysis, a fourth may be found directly in the excitement of the ovarian plexus of nerves. This evolution of nerve-force which accompanies the maturation of the ovule, is the immediate cause of the afflux of blood to the utero-ovarian vessels. The effect upon the latter is probably due to the spinal nerve-fibres contained in the plexus, and upon which the ganglionic excitement acts like the galvanism in Schiff's experiment, already described. Direct stimulation of the vaso-motor nerves, alone, as has been said, contracts the blood-vessels. Stimulation of the spinal fibres associated with them exercises the contrary effect. An excessive stimulation of those fibres which enter into the ganglionic masses, would have an effect similar to that of excessive stimulation directly addressed to the cerebro-spinal system, and the blood-vessels would be not only dilated, but paralyzed.
Among the conditions, therefore, which may, by inducing either pain or excessive hæmorrhage, 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 hæmorrhage; 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: