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being covered in the rest of their course by the obliquus. They are easily discovered at the outer margin, and the excitation of each nerve produces contraction of the corresponding belly of the muscle. The upper portions draw the abdominal wall upwards, and those below the umbilicus draw it downwards. The nerves of the external oblique muscle are to be sought in the lower intercostal spaces, at the origins of the upper digitations of the muscle. Press the electrodes deeply at the free ends of the eleventh and twelfth ribs. There will follow considerable flattening of the abdomen in the region of the contracting portion.
The transversalis is powerfully influenced by pressing an electrode on the soft parts on both sides above the crista ilii, near the outer margin of the quadratus lumborum, but even in thin persons this is not always easy. With a strong current, if success is obtained, the action is as powerful as in the strongest voluntary efforts to empty the rectum or bladder.
Of the muscles of the back the splenius capitis may be excited at its outer margin. A powerful rotation of the head towards the same side is produced. The other deeper muscles of the neck are beyond reach.
The latissimus dorsi, together with the teres major and teres minor, and serratus posticus inferior are generally only accessible to intramuscular excitation.
The Inferior Extremity. The crural nerve, after its passage under Poupart's ligament, lies wholly superficial in the groove of the iliac muscle, and is accessible for some distance. Its excitation produces very energetic extension of the leg, with severe pain in the course of the greater and lesser saphena nerves, and of the anterior and middle cutaneous femoral, that is on the front and inner side of the thigh, the knee and inner side of the leg as far as the great toe. Its motor branches can be isolated only in thin persons, but direct excitation of the muscles near the points of entrance of their nerves always produces a powerful effect.
The obturator nerve, or at least the mesh of its twigs, since it divides in the obturator foramen, may be reached from the foramen. Place the electrode perpendicularly upon the horizontal ramus of the pubes and strongly compress the skin, fat, and pectineus muscle against the bone. This produces very powerful abduction of the thigh, but it is very painful, partly because the skin is richly supplied with sensitive filaments from the genito-crural nerve, and partly because the obturator itself consists largely of sensitive fibres destined to supply the knee and the inner surface of the thigh.
The superior gluteal nerve is withdrawn by its deep position from direct excitation, as is also the inferior gluteal.
The sciatic nerve, although covered by the thick flexor muscles of the leg, may yet be reached at the lower margin of the gluteus maximus in the middle point between the great trochanter and the tuber ischii, by using firm pressure with a strong electrode, covered by a rather large cushion of sponge or leather. There results a powerful flexion of the leg and contraction of all the muscles of the leg and foot, with acute pain in all the parts receiving sensitive fibres from the nerve.
The peroneal nerve may be reached directly it is given off from the sciatic, on the inner margin of the biceps femoris and of its tendon. The excitation is much more certain and precise at the back of the prominence of the head of the fibula, which affords firm resistance to the pressure of the electrode. In this position also the external and middle sural cutaneous nerves, being given off by the peroneal, above the head of the fibula, escape the action of the current. There results contraction of the peronei, tibialis anticus, extensor digitorum longus and brevis, and extensor pollicis longus, with sensation in the cutaneous nerves of back of the foot.
The tibial nerve, after the division of the peroneal lies in the ham covered only by the popliteal fascia, the skin and a thin layer of fat. From the
From the power of compressing it against a resisting surface it may be excited with as much certainty as the peroneal. There results an energetic contraction of all the muscles of the back of the leg and the sole of the
foot with painful sensations in the sural nerve and in the sensitive branches of the external and internal plantar. The tibial nerve after emerging from behind the belly of the soleus may be found in the middle line between the inner margin of the tibia and the tendo Achillis, and may be followed downwards as far as the posterior border of the internal malleolus. Contraction of all the muscles of the sole of the foot results, and painful sensations in the plantar digital nerves.*
ELECTRIZATION OF THE CENTRAL ORGANS OF THE
NERVOUS SYSTEM. The central organs of the nervous system, as well as the nerve trunks that pass through the great cavities, on account of being completely surrounded by soft parts and bones which cannot be forced into contact with them by external compression, are withdrawn from the influence of the faradic current, unless it be used of excessive strength. On the other hand an indirect excitation of the brain through the nerves of special sense, especially the optic and auditory, may be accomplished by voltaic currents of medium strength. Besides intense sensations of light and abnormal sensations of sound, excitation of these nerves with strong currents may be followed by vertigo, or even loss of consciousness; and in exciting them the utmost circumspection is all the more necessary since the amount of reaction displayed by different people is widely different.
* For full details regarding the isolation of single muscles and their physiological action, consult Ziemssen, Die Electricität in der Medizin. Berlin, 1866; and Duchenne, Physiologie des Mouvements. Paris, 1857.
When it is desired to act only upon the skin faradization has many advantages over the other forms of electricity, and in practice it is invariably preferred. There are three methods of applying it.
1. The electric hand.—A moist rheophore (a sponge contained in a cylinder), as shown in fig. 28, is applied to some little sensitive part of the patient's body, the other rheophore is held by the operator, who passes the back of his disengaged hand over the points which he wishes to excite.
2. Solid metallic rheophores.—The rheophores, figures 28, 29, 31, and 32, without sponges or leathers, and being quite dry, are applied by their metallic surfaces to the skin, and either kept stationary or moved over it with greater or less rapidity, in proportion to the degree of irritation it is required to produce. If the conical rheophore is maintained for some time immovable, it is termed the electric nail, from its action somewhat resembling a hot nail penetrating the skin.