The feature of Jacksonian epilepsy to which I wish to call attention is the periodicity of the discharge. Whether we regard the lesion as “irritative” or “discharging,” it is, at all events, chronic; and whether we regard the discharges as going direct from the cortex to the efferent nerve-cells, or as causing convulsions in a more roundabout way through subcortical systems, they are, at all events periodic. How, then, do chronic lesions cause periodic discharges ? The answer which I wish to put forward is suggested by certain passages in Mercier's Psychology, Normal and Morbid, p. 283, which run as follows: —Speaking of how organic bodies may contain a store of motion which can be liberated by the impress of motion from without, and after likening this property to that of animals and their power of movement, the author continues, “But animal organisms have a further property which most inorganic bodies have not. They are continually adding to their stores of motion, and by these continual additions their store at length becomes surcharged. The tension of the contained motion reaches such a pitch that the containing resistance is no longer sufficient to keep it in bond, and it breaks out, possibly without the provocation of added motion, certainly with minimal provocation.’’ Later on, when discussing “Will and Desire,” the same author writes of nervous mechanisms, “There are many machines used in the arts, which depend for their actuation on the gradual filling of a vessel with water. The vessel is of such a shape and so supported that, as it fills, the centre of gravity shifts, until, at a certain degree of fulness, the vertical at the centre of gravity falls without the base; the vessel then capsizes, empties its contents, regains its previous distribution of weights, rights itself, and begins to fill once more.”
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