554 



ELECTRICAL CURRENTS IN NERVE AND MUSCLE. 



pole of the battery, while the platinum wire (d) is connected with the negative pole of the 

 "battery."] 

 331. ELECTRICAL CURRENTS in PASSIVE MUSCLE and NERVE SKIN CURRENTS. 



-Methods. In order to investigate the laws of the muscle-current, we must use a muscle 

 oompoeed*of parallel fibres, and with a simple arrangement of its fibres in the form of a prism 

 or cylinder (fig. 399, I and II). The sartorins muscle of the frog supplies these conditions. In 

 such a muscle, we distinguish the surface or the natural longitudinal section, its tendinous 

 ends or the natural transverse section ; further, when the latter is divided transversely to the 

 long axis, the artificial transverse section (fig. 399, I, c, d); lastly, the term equator (a, b-m, n) 

 is applied to a line so drawn as exactly to divide the length of the muscle into halves. As the 

 currents are very feeble, it is necessary to use a galvanometer with a periodic damped magnet 

 (figs. 380, I, and 387), or a tangent mirror-boussole similar to that used for thermo-electric 

 purposes (fig. 230). The wires leading from the tissue are connected with non-polarisable elec- 

 trodes (fig. 380, P, P). 



The capillary-electrometer of Lippmann may be used for detecting the current (fig. 400). 

 A thread of mercury enclosed in a capillary tube and touching a conducting fluid, e.g., dilute 



sulphuric acid, is displaced by 

 the constant current, in conse- 

 quence of the polarisation tak- 

 ing place at the point of contact 

 altering the constancy of the 

 capillarity of the mercury. The 

 displacement of the mercury 

 which the observer (B) detects 

 by the aid of the microscope 

 (M) is in the direction of the 

 positive current. R is a capil- 

 lary glass tube, filled from 

 above with mercury, and from 

 below with dilute sulphuric 

 acid. Its lower narrow end 

 opens into a wide glass tube, 

 provided below with a platinum 

 wire fused into it and filled 

 with Hg (q), and this again is 

 covered with dilute sulphuric 

 acid (s). The wires are con- 

 nected with non-polarisable 

 electrodes applied to the + and 

 - surfaces of the muscle. On 

 closing the circuit, the thread 

 of mercury passes downwards 

 from c in the direction of the 

 Capillary electrometer, arrow. 

 R, mercurv in tube; C ompe nsa tion. T h e 

 capillary tube ; s, sul- strength of the current in ani- 

 phuric acid ; q, Hg ; Tna ^ tissues is best measured by 

 B, observer ; m' mi- tne compensation method of 

 croscope. Poggendorf and du Bois-Rey- 



, mond. A current of known 



strength or which can be accurately graduated, is passed in an opposite direction through the 

 same galvanometer or boussole, until the current from the animal tissue is just neutralised or 

 compensated. [\\ hen this occurs, the needle deflected by the tissue-current returns to zero. 

 1 he principle is exactly the same as that of weighing a bodv in terms of some standard weights 

 placed m the opposite scale-pan of the balance.] 



[Hermann calls the current obtained from an injured muscle, i.e., one on which 

 an artificial transverse or other section has been made, a demarcation-current, 

 while the currents obtained when such a muscle contracts, he calls action-currents. 

 This section deals with demarcation-currents, or the muscle-current of du Bois- 

 Reymond.] 



1. Perfectly fresh uninjured muscles yield no current, and the same is true of 

 dead muscle (L. Hermann, 1867). 



2. Strong electrical currents are observed when the transverse section of a muscle 

 is placed on one of the cushions of the non-polarisable electrodes (fig. 380, I, M), 



Fig. 400. 



Fig. 399. 

 Scheme of the muscle-current. 



