LIVING TOKPEDOS IN BERLIN. 539 



17. On the secondary electromotive phenomena in the 

 electrical nerves of the Torpedo. 



I endeavoured to answer the question as to the secondary electro- 

 motive behaviour of the electrical nerves in the second fish. It will 

 be remembered that in the paper on the secondary electromotive 

 phenomena of muscles and nerves, it is stated that positive polarisa- 

 tion by the ascending current, exceeds very uniformly that due to 

 the descending- current in the posterior roots of the spinal nerves of 

 the frog-. If here also we denote the physiological direction of 

 action of the roots as homodromous, and the opposite as hetero- 

 dromous, then positive polarisation in the homodromous direction 

 is stronger than in the heterodromous. On the other hand, the 

 corresponding difference in the case of the anterior roots is not so 

 clear, and if at first it is seen, it is soon effaced ; i. e. positive 

 polarisation in the homodromous, here the descending direction, does 

 not exceed perceptibly or not permanently that in the heterodro- 

 mous, here the ascending direction 1 . On account of the great 

 difficulty which attends these experiments on the roots, owing to 

 their shortness and delicacy, it appeared extremely desirable to 

 repeat these experiments on the electrical nerves, which, according 

 to general opinion, can be obtained almost or wholly centrifugal, 

 and of a length and thickness, such as is not to be met with in the 

 animals which have hitherto been available for physiological expe- 

 riment. I stated in the first communication (p. 463) that they can 

 be easily found unbranched of a length of 3-4 cm., but I have since 

 had them as long as 5-5 cm. with a thickness of 2-5 mm. 



The nerves were laid in a groove, which was cut with a three- 

 cornered file in a piece of cork afterwards varnished. The clay 

 shields of the leading-in pads of the battery circuit were put upon 

 the two transverse sections. The clay points of the unpolarisable 

 tube electrodes, as terminals of the galvanometer circuit, were placed 

 on symmetrical points of longitudinal section near both transverse 

 sections. With this arrangement, the axial current made itself 

 uniformly perceptible with a force of 0-00125 to 0-00313, corre- 

 sponding as closely as possible to the difference recorded on p. 537. 

 The galvanometer S had 10,000 turns at zero distance, and the 

 galvanometer P 50 turns at 20 mm. distance. I obtained the fol- 

 lowing numbers : 



1 Gesammelte Abhandlungen, 1883, vol. i. pp. 382-387. 



