38 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



experiments that the tetanus which results from closing a strong current 

 remains located at the kathode, and the tetanus following the opening of 

 the current remains located at the anode. 



The same is true of the nerve as of the muscle; the irritating process which 

 is called out by the sudden entrance of a battery current into a nerve starts 

 from the negative pole, the kathode, and spreads thence throughout the nerve, 

 while the irritating process excited by the cessation of the flow of the current 

 starts from the region of the positive pole, the anode, and spreads from that 

 point throughout the nerve. A proof of this was obtained by Von Bezold, 

 who observed the difference in the time between the moment of excitation and 

 the beginning of the contraction of the muscle, when the nerve was excited 

 by opening and by closing the current, with the anode next to the muscle, 

 and with the kathode next to the muscle. He found the time to be longer 

 when the current was closed if the kathode was the more distant, and to be 

 longer when the current was opened if the anode was farther from the muscle. 

 Evidently in the case of the nerve as of the muscle, the irritable substance 

 subjected to the current is not all affected alike. The current does not 

 set free the irritating process at every part of the nerve, but produces 

 peculiar and different effects at the two poles, the change which occurs at the 

 kathode when the current is closed being of a nature to cause the development 

 of the excitatory process which awakens the closing contraction, and the 

 change which occurs at the anode when the current is opened being such a? 

 to cause the development of the excitatory process which calls out the opening 

 contraction. 



Closing contractions are stronger than opening contractions. The irritation 

 developed at the kathode is stronger than that developed at the anode. It is 

 true of both striated and unstriated muscles that an efficient irritation can be 

 developed at the kathode with a weaker irritant than at the anode. Moreover, 

 a greater strength of current is required to produce opening than closing con- 

 tinued contractions. 



The same may be said of nerves. If one applies a very weak battery cur- 

 rent to the nerve of a nerve-muscle preparation, he notices when he closes the 

 key a single slight contraction of the muscle, and when he opens the key, no 

 effect. If he then increases the strength of the current very gradually, and 

 tests the effects of the making and breaking of the current from time to time, 

 he observes that each time the strength of the current is increased the closing 

 contraction, which is due to irritation originating in the part of the nerve sub- 

 ject to the kathode, grows stronger, and finally contractions are also seen when 

 the circuit is broken, the irritation process developed at the anode having 

 become strong enough to excite the muscle. These opening contractions at 

 first are weak, but gradually increase in strength, until with a medium strength 

 of current vigorous contractions are seen to follow both opening and closing of 

 the current. If the strength of the current be still further increased, it is 

 found that either the closing or opening contraction begins to decrease in 

 size, and if a very strong current be employed, the closing or opening con- 



