MUSCLES, NERVES, AND ELECTRICAL ORGANS. 171 



pads l were applied to the internal (that is, femoral) side of the 

 muscles ; through these pads the polarising- current entered the 

 muscles. Between their edges, the edges of the pads which led off 

 the polarisation current to the galvanometer were in contact with 

 the external side. On account of the resistance of the tendons, 

 which are apt to get dry, it is not feasible to conduct the 

 current to the muscles through the fragments of bone outside of 

 the ivory plates, which would have been in many respects a far 

 better mode of proceeding. Both pairs of electrodes, which in 

 the following pages will be called for shortness sake battery- 

 pads and galvanometer-pads, are covered with clay, which is often 

 renewed. 



In consequence of the very small duration of most of the ex- 

 periments, errors consequent on external secondary resistance are 

 scarcely to be apprehended ; at all events, if they exist, they can be 

 readily recognised. The muscle-current was compensated, with the 

 aid of the round compensator, by a derivation-current from a 

 Raoult's battery 2 . 



In the experiments on nerves the two sciatic nerves of the same 

 frog were commonly used as one. They were secured to the upper 

 surfaces of two pieces of cork with insect needles, and gently ex- 

 tended by shoving the corks along a horizontal glass rod ; the two 

 pairs of electrodes were applied in the same way as in the case 

 of the muscle. In the experiments on the roots of the spinal nerves, 

 unpolarisable tube electrodes with clay tips (Stiefelelektroden] were 

 sometimes used s at other times special contrivances 3 . 



A condition essential to certainty of results in these experiments 

 which is difficult to secure, is that of complete insulation of the 



1 Gesammelte Abhandlungen, vol. i. pp. 88, 89. 



2 Untersuchungen am Zitteraal, p. 141. 



3 Since my last publication of an experimental character, a phenomenon connected 

 with the Thonstiefeln has come under my notice, which not only deserves considera- 

 tion in using this form of non-polarisable electrodes, but is on other grounds interesting. 

 If you have a pair of such tubes, the freedom of which from polarisation you have 

 ascertained by bringing the tips into contact, and then touch the thick upper part 

 (Wulsf) of the one with the tip of the other, a current is found to exist of which the 

 direction is from the tip to the ' Wulst? This action is less marked in fresh tubes 

 than in tubes that have been prepared for some time. This may be explained on the 

 assumption that there is an electromotive action between moist and less moist clay, 

 though in a series of layers of clay of different degrees of moisture there is no grada- 

 tion of tension. Moist clay brought into contact with less moist between zinc pads 

 gives an e.m.f. amounting to 0-014 Raoult. The relation of the electromotive action 

 between clays of different degrees of moisture to the clay thermal currents of Nobili 

 has not yet been explained. (Untersuchungen, vol. ii. part i. pp. 201-203.) 



