644 UNPOLARIZABLE ELECTRODES. SECONDARY RESISTANCE. 



ever, attracts hydrogen, but the latter at once in the nascent state reduces 

 the copper from its combination to metallic copper, which accumulates on the 

 copper plate as a bright deposit. The electromotor force of a Daniell cell 

 varies, in accordance with the degree of amalgamation of the zinc and the con- 

 centration of the fluid, between 0.909 and 1.35 volts, the internal resistance 

 being 2.8 ohms. 



If the electrodes of a constant element be conveyed to a moist animal tissue, 

 for example nerve or muscle, electrolysis and, as a result, polarization must, 

 naturally, at once take place. In order to avoid this, unpolarizable electrodes have 

 been constructed (Fig. 225, IV). As a result of the studies of Regnauld, Matteucci, 

 and du Bois-Reymond, it has been determined that such electrodes can be con- 

 structed if the conducting wire coming from each element be first connected 

 with an amalgamated plate of zinc (z, z), the latter being secured (k, k) in a tube 

 filled with a solution of zinc sulphate (a a), whose lower extremity is closed 

 by means of an inverted cone of clay (t, t) moistened with 0.6 solution of sodium 

 chlorid. If these clay points are applied to the tissues, no polarization takes place 

 or at most only a very slight amount. 



Exactly the same device is employed for examining the currents in muscles 

 and nerves (Fig. 225, I). As these tissues when in direct connection with metals 

 generate currents, a similar non-polarizable device is employed, but under such 

 circumstances it has a somewhat different form. It consists of cups of zinc (P, P) 

 filled with concentrated acid-free zinc-sulphate solution (s, s). In each cup is 

 immersed a pad of blotting paper (b, b), which is saturated by the zinc-solution. 

 Finally, this is covered with a thin layer of plastic clay (t, t) moistened with 0.6 

 percent, sodium-chlorid solution, which protects the tissues from the direct caustic 

 effects of the dissolved zinc salt. 



Nerve-fibers and muscle-fibers, as well as moist vegetable tissues, fibrin, and 

 similar bodies, which have a porous structure filled with fluid, likewise exhibit 

 the phenomena of polarization on the application of currents of considerable 

 strength, and this has been designated internal polarization of moist conductors. 

 It is believed that the better-conducting solid particles in the interior of these 

 bodies exert an electrolytic effect upon the particles of fluid in contact with them, 

 as do metallic electrodes in contact with fluid. The ions resulting from the dis- 

 integration of the particles of the internal fluid would then give rise to the internal 

 polarization in consequence of the tension existing between them. The con- 

 duction-resistance of muscle and nerve depends, according to Hermann, in part 

 upon polarization. He considers the marked polarization of animal tissues (only 

 comparable with that of the metals) as a specific vital property of protoplasm. 



If the two electrodes of the cell are introduced into the divisions of a 

 fluid separated into two halves by a porous partition, it will be observed that 

 particles of fluid are conveyed in the direction of the galvanic current, from the 

 positive to the negative pole, so that after the lapse of some time the amount 

 of fluid in one half of the vessel has diminished, while that in the other half 

 has increased. This phenomenon of direct transference has been designated the 

 cataphoric effect. Upon it depends the galvanic transference of soluble sub- 

 stances through the external integument. Upon this depends, apparently, also 

 the phenomenon of so-called secondary external resistance. If the copper electrodes 

 of a strong constant cell are each introduced into a vessel filled with copper- 

 sulphate solution, from which projects a pad saturated with this fluid, and if 

 further over this pad is placed a bit of muscle, cartilage, vegetable tissue or a 

 prismatic strip of coagulated albumin, it will be seen that after closure of the 

 circuit the current undergoes considerable enfeeblement. If the current be now 

 reversed, its strength is at first increased, but later it declines from the maximum. 

 Thus, a constant alternating reversal of the current gives rise to similar alternation 

 in the variation of the current. If a prismatic bit of albumin has been used in 

 the experiment, it will be observed that simultaneously with the enfeeblement of 

 the current the albumin has become deficient in water and presents a shrunken 

 appearance in the vicinity of the positive pole, while, conversely, the albumin 

 applied to the negative pole (probably through cataphoric action) is swollen and 

 contains more water. If the direction of the current be altered the same phe- 

 nomena is observed, but at the opposite poles. The contraction and loss of water 

 in the albumin at the positive pole described must be the cause of the resistance 

 in the circuit that explains the enfeeblement of the galvanic current. This phe- 

 nomenon is designated that of secondary external resistance. 



