162 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



blocked (katelectrotonus). The action of the various 

 ions on nerve-elements is as yet unknown. The other 

 effect of the current may consist in the migration of 

 certain colloids in one direction and of water in the 

 other direction. 



If in the larvae of Amblystoma the tension of the 

 flexors of the spinal column predominates in a de- 

 scending current (from head to tail) and the tension 

 of the extensors of the spinal column predominates in 

 an ascending current, this proves that the nervous ele- 

 ments of the flexors and extensors in the central ner- 

 vous system, whicJi are affected by the ions, possess an 

 opposite orientation. Maxwell and I have developed 

 more definite ideas concerning the orientation of these 

 elements, but such details are for the time being of 

 minor importance. I only wish to state that the rela- 

 tive orientation of these elements must be the same 

 in every segment of the spinal cord ; for when the 

 spinal cord in the larvae of Amblystoma is severed or 

 the whole animal cut into several pieces the effects 

 of the current remain the same. Since the article 

 mentioned above was published I have found that 

 crayfish (young and small specimens were used for 

 these experiments) behave toward the current like 

 Amblystoma larvae. If the median-plane of the 

 crayfish is in the direction of the lines of the current 

 (which are all straight and parallel in these experi- 

 ments) and the head is turned toward the anode, the 

 flexors of the body contract and the crayfish rolls it- 

 self into a complete ring, provided that the density of 



