ELECTRICAL CURRENTS OF ACTIVE MUSCLE. 557 



Frog Current. It is asserted that the total current in the body is the sum of the electrical 

 currents of the several muscles and nerves which, in a frog deprived of its skin, pass from the 

 tip of the toes toward the trunk, and in the trunk from the anus to the head. This is the 

 " corrente propria della rana" of Leopoldo Nobili (1827), or the "frog current" of du Boisr 

 Reymond. In mammals, the corresponding current passes in the opposite direction. 



After death, the currents disappear sooner than the excitability (Valentin) ; they remain 

 longer in the muscle than the nerves, and in the latter they disappear sooner in the central 

 portions. If the nerve-current after a time become feeble, it may be strengthened by making 

 a new transverse section of the nerve. A motor nerve completely paralysed by curara gives a 

 current (Funke), and so does a nerve beginning to undergo degeneration, even two weeks after 

 it has lost its excitability. Muscles in a state of rigor mortis give currents in the opposite 

 direction, owing to inequalities, which take place during decomposition. The nerve-current is 

 reversed by the action of boiling water or drying. 



Currents from Skin and Mucous Membranes. In the skin of the frog the 

 outer surface is + , the inner is - (du Bois-Reymond), and the same is true of the 

 mucous membrane of the intestinal tract (Eosent/tal), the cornea (Grunhagen), as 

 well as the non-glandular skin of fishes (Hermann) and molluscs (Oehler). Currents 

 are also manifested by glands. 



332. CURRENTS OF STIMULATED MUSCLE AND NERVE ACTION- 

 CURRENTS. 1. Negative Variation of the Muscle-Current. If a muscle, which 

 yields a strong electrical current, be thrown into a state of tetanic contraction by 

 stimulating its motor nerve, then, when the muscle contracts, there is a diminution 

 of the muscle-current, and occasionally the needle of the galvanometer may swing- 

 almost to zero. This is the " negative variation of the muscle-current " (du Bois- 

 Reymond). It is larger, the greater the primary deflection of the galvanometer 

 needle and the more energetic the contraction. 



After tetanus, the muscle-current is weaker than it was before. If the muscle was so placed 

 upon the electrodes that the current was "feeble," equally during tetanus there is a diminution 

 of this current. In the inactive arrangement, the contraction of the muscle has no effect on 

 the needle. If the muscle be prevented from shortening, as by keeping it tense, the negative 

 variation still takes place. 



2. Current during Tetanus. An excised frog's muscle tetanised through its 

 nerve shows electro-motive force the so-called " action-current." In a tetanised 

 frog's gastrocnemius, there is a descending current. In completely uninjured human 

 muscles, however, thrown into tetanus by acting on their nerves, there is no such 

 current (L. Hermann); similarly, in quite uninjured frog's muscles, as well as when 

 these muscles are directly and completely tetanised, there is no current. 



3. Current during the Contraction-Wave. If one end of a muscle be directly 

 excited with a momentary stimulus, so that the contraction-wave ( 299) rapidly 

 passes along the whole length of the muscular fibres, then each part of the muscle, 

 successively and immediately before it contracts, shows the negative variation. 

 Thus, the "contraction-wave" is preceded by a "negative wave" of the muscle- 

 current, the latter occurring during the latent period. Both waves have the same 

 velocity, about 3 metres per second. The negative wave, which first increases and 

 then diminishes, lasts at each point only 0*003 second (Bernstein). 



4. During a Single Contraction. A single contraction also shows a muscle- 

 current. [The electrical variation takes place during the latent period of the 

 muscular contraction, so that it precedes the latter. The variation begins "01" to 

 04" after excitation, while the contraction does not begin until '11" to "33" 

 (Waller). A frog's muscle may be made to record its contraction, and simul- 

 taneously the variation of the electrical current, as ascertained by the capillary 

 electrometer, may be photographed (fig. 403), and the same may be done in the 

 case of the heart (fig. 404). The capillary electrometer may with advantage be 

 employed to measure this time-difference, the electrical and the mechanical events 

 being simultaneously recorded.] 



The diphasic variation 1st phase middle negative to end ; 2nd phase and negative to 

 middle begins about *01" before the commencement of muscular contraction ( Waller). 



