Many others have written upon this subject, but upon the probable pathology they have been silent.
The experiments recently made by Dercum and Parker88 on the artificial induction of convulsive seizures are of considerable interest, and certainly tend to throw light on the point in question. These convulsions were produced by subjecting a group of muscles to a constant and precise effort, the attention being at the time concentrated upon some train of thought. The position most frequently adopted was to cause the arms to be held so that the tips of the fingers barely touched the surface of the table before which the subject was seated, the fingers not being allowed to rest upon the table, but maintained by a constant muscular effort barely in contact with it. After this position was maintained for a variable length of time tremors commenced in the hands; a little later these tremors became rapidly magnified into rapid movements of great extent sometimes to and fro, sometimes irregular; if the experiment was carried still farther, the muscles of the arms, shoulders, back, buttocks, and legs become successively affected, and the subject was frequently thrown violently to the ground in a strong general convulsion, the consciousness being always retained.89 The more frequently these experiments were performed, the more readily the seizures were brought on, and, other things being equal, with successively increasing intensity. One subject thus experimented upon became so susceptible that the jar of a passing wagon sufficed to induce a partial seizure. These experiments throw a new light upon the associated movements previously mentioned, and show how easily the phenomena noticed in one part may pass to another having physiological relationship with it. It is highly probable that some nutritional change in the cord would follow the too frequent repetition of these experiments.
88 “The Artificial Induction of Convulsive Seizures,” Dercum-Parker, The Polyclinic, Philada. 1884, vol. ii. pp. 95-97.
89 These experiments were subsequently repeated before the Philadelphia Neurological Society in 1885.
Peripheral pathological conditions undoubtedly exist in many cases of copodyscinesia; these may be so slight that they can scarcely be demonstrated, or, on the other hand, they may be marked, and even present a well-marked inflammation of one or more of the nerves of the arm, as evidenced by pain on motion, tenderness on pressure, and sensory and nutritive disturbances in the areas which they supply.
There are some cases where the disability is pronounced, and yet the most careful examination fails to reveal peripheral changes of sufficient gravity to account for the severity of the symptoms; these, in my opinion, are best explained by supposing a hyperexcitability of the spinal centres, as previously expressed.
The electrical reaction in many cases tends to prove an irritable condition of the spinal centres. In most of the cases of the spastic group there will be found a quantitative increase in the reaction of both nerve and muscle to the galvanic current. Gowers90 states that he has found such an increase in diseases regarded as functional, as paralysis agitans and chorea, and considers it an interesting proof of the molecular changes which underlie or result from functional maladies. He previously remarks91 that such a condition of exalted irritability is to be ascribed to a corresponding change in the nutrition of the nerve-cells of the spinal cord, secondary to the irritative influence which caused it.
90 Dis. of Spinal Cord, 2d ed., Philada., 1881, p. 40.
91 Med. Times and Gaz., London, vol. ii., 1877, p. 536.
Erb92 also considers that quantitative increase in the electrical reaction points to central lesion. Buzzard93 quotes several authors upon tetany—which some cases of copodyscinesia closely resemble—who state that the electrical reactions are increased quantitatively in that affection, and considers, himself, that the change is due to central lesion.