Nervous and mental diseases . nic current one must be sure of the pole ELECTRICAL CONDITIONS. 45 with which he is operating. The negative pole can be readily determinedby bringing both metal terminals into contact with a piece of wet litmuspaper which shows the characteristic acid red color at the spot touched bythe negative end. Or both metal terminals of the conducting cords maybe placed in a little water. The decomposition of the water at the negativepole is evident in the formation of numerous fine gas bubbles. When the active electrode is applied over the belly of a givenmuscle, a muscula
Nervous and mental diseases . nic current one must be sure of the pole ELECTRICAL CONDITIONS. 45 with which he is operating. The negative pole can be readily determinedby bringing both metal terminals into contact with a piece of wet litmuspaper which shows the characteristic acid red color at the spot touched bythe negative end. Or both metal terminals of the conducting cords maybe placed in a little water. The decomposition of the water at the negativepole is evident in the formation of numerous fine gas bubbles. When the active electrode is applied over the belly of a givenmuscle, a muscular contraction is set up by the faradic current, thesame as that produced by stimulating the nerve-trunk. If the currentbe not too strong and the electrode not too large, the effect may belimited to the given muscle, or to a portion of a muscle. Every mus-cle may also be actuated by the galvanic current by applying the active N. cruralis N. obturatorM. pectineus M. adductor magnusM. adduct. longus M. cruralisM. vastus internus. VM. tensor fascise latse M. sartorius M. quadriceps feuioris M. rectus femoris M. vastus externus Fig. 11.—Nerves and motor points in lower extremity. pole on the point corresponding anatomically to the entrance of itsmotor nerve. A familiarity with motor p>oints is of practical are shown in the accompanying diagrams. Slight variations intheir location are common, and several trials are often required to findthem. It is well to mark with a lead-pencil the necessary points,if repeated tests are to be employed. The galvanic polar responsesare, in healthy muscles, identical with those obtained through the nerve-trunks. In Disease.—Diseases changing the nutrition and structure of thelower motor neuron, which consists of the spinal cell-body and its peripheralprojection and termination in muscular tissue, alter not only the trophicconditions over which the neuron presides, but also interfere with its 46 NERVOUS AND MENTAL DISEASES. elect
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