387 



or absence of differential deflection of the needle will show whether 

 any or what degree of effect has been produced oil the secondary 

 electromotor power of the altered nerve. In this way the author 

 found that both the cold of a refrigerating mixture and a heat of 

 from 50 to 60 Cent, caused a great diminution of the secondary 

 current in the nerves of a fowl. It is greatly weakened also by 

 crushing the nerve, or by keeping the nerve long immersed in di- 

 stilled water ; immersion for a few seconds has no appreciable effect. 

 Immersion for a few minutes in alcohol, or in a solution of potash 

 of gp^Q strength, entirely extinguishes the secondary current. Two 

 nerves subjected to the same exciting current, the one fifteen or 

 twenty minutes after the other, show no difference in their secondary 

 currents. If an exciting current is passed through a nerve, first in 

 one direction and then for an equal time in the opposite direction, 

 the secondary current produced is weaker than if the pile-current had 

 been in one direction only. The secondary current increases, within 

 certain limits, with the duration, and also with the intensity of the 

 pile-current. Neither the size nor the number of the nerves (if united 

 by superposition) exercises any influence. Four similar nerves were 

 subjected to the same pile- current ; three of these nerves superposed 

 were then placed in opposition to one as a differential pile, but no 

 differential current was produced. Portions of nerve of equal length 

 from a frog, a lamb, and a fowl, were subjected to the same pile- 

 current, and when afterwards opposed successively, the one to the 

 other, gave no differential current ; yet singly each gave a secondary 

 current of 40 or 50. A decided effect, however, is produced by 

 the length of the nerve ; when pieces of different lengths were com- 

 pared, a strong differential current was constantly found to corre- 

 spond with the longest portion of nerve ; the author remarks that 

 this result cannot be understood, unless we admit that the secondary 

 electromotor power, which is originally greatest in contact with the 

 electrodes, extends successively to all the parts of a nerve traversed 

 by the pile-current. 



The author then comes to the fact which he conceives to be of 

 greatest importance, in the application of the doctrine of the secondary 

 electromotor power of nerves to the explanation of certain electro- 

 physiological phenomena. It is expressed in the following proposi- 

 tion : 



