357 



Eckardt, is to be found in an experiment which may be illustrated 

 by means of the two following figures. In this experiment, the 

 nerve of a properly prepared frog's leg is placed, one portion (that 

 nearest to the leg) across the poles I I' of an induction coil, another 

 portion across the poles P N of a galvanic apparatus. Having done 

 this, the leg is first thrown into a state of tetanus by passing a series 

 of induced currents, and then (the tetanizing influence still con- 

 tinuing in operation) the continuous current of the galvanic apparatus 

 is transmitted from P to N. This is the experiment. The result 

 is that the tetanus ceases when, as in fig. 7, the inverse current 



Fig. 7. 



passes, and continues when, as in fig. 8, the direct current passes. 

 Nor is this result altered by inverting the order in which the con- 



Fig. 8. 



tinuous and induced currents are made to act upon the nerve. Thus 

 the induced currents produce contraction if applied after the direct 

 continuous current, but not if applied after the inverse continuous 

 current. Nay, it would even seem as if the direct current is actu- 

 ally favourable to contraction ; for a solution of salt, which of itself 

 is too weak to produce tetanus when applied to a nerve, will have 

 this effect when a direct current is made to pass through another 

 portion of the same nerve. In performing this experiment, Professor 

 Eckardt proceeds as follows: First of all he tetanizes a frog's 

 hinder limb by placing a portion of the nerve nearest to it in a strong 

 solution of salt ; after this he adds water until the strength of the 

 saline solution is no longer sufficient to keep up a state of contraction 

 in the muscles ; then, all things being as they were, he passes the 

 direct current through a portion of nerve which is not immersed in 

 the solution. The result is that the tetanus immediately returns. 



