MUSCLES, NERVES, AND ELECTRICAL ORGANS. 209 



endeavours to procure them have been fruitless. The optic nerve of 

 a large osseous fish ought to be an excellent object for the fibres 

 which conduct centripetally, but this I have not yet found time to 

 try. For fibres having a physiological centrifugal action there seems 

 to be nothing better than the electric nerves of a Torpedo. I will 

 not say anything of an abundance of other experiments which are 

 here suggested. Even the experiments already communicated seem 

 well deserving of the attention of physiologists. They present the 

 first example of an electromotive difference between centrifugally 

 and centripetally acting fibres. One might well in this case em- 

 ploy the expression of which Paul Erman made use with reference 

 to the law of contraction : ' The mere suspicion of such a difference 

 inspires awe V One must therefore be all the more cautious. Even 

 if the supposed law were demonstrated, it remains to be con- 

 sidered whether it must be regarded as an action of the physiological 

 innervation wave, or a provision for facilitating its propagation in a 

 definite direction. I once doubted its existence or even its possi- 

 bility on theoretical grounds 2 . 



18. On the influence of various conditions on the Polarisation 



of Nerves. 



Regarding the question of the conditions which influence the 

 polarisability of nerves, I have scarcely any results which are 

 methodically arranged. Matteucci already knew that nerves 

 which have been exposed to boiling-heat do not any longer 

 show a negative after-current (Sect. 14). If, however, the nerves 

 are protected from drying and allowed gradually to die at a low 

 temperature, they retain their secondary electromotive action for 

 a long time but with decreasing strength. Even after one-and- 

 twenty hours a trace of polarisation could be seen. For example, 

 after this length of time, sensory roots which had lain undisturbed 

 in the moist chamber gave with 2 Groves and o^>o^i time of 

 closure : 



The experiments belong to the same series as those last com- 

 municated. After twenty-seven hours, however, there followed 

 only purely negative polarisation : 



T-9l -9T-91-9J 



1 Untersucliungen iiber thierische Elektricitat, vol. i. p. 334. 



2 Ibid. vol. ii. part i. pp. 574, 575. 



P 



