1876.] 



Excitability of Motor Nerves. 



15 



of the extreme nerve-section, that if the nerve, while hanging in a vertical 

 direction over the flat surface of the clay bridge, be lowered until the sec- 

 tion just touches the flat surface of the clay, it may frequently be ob- 

 served that the attached muscle responds to make and to break of the 

 current. Yet this must be a case of almost complete transverse stimula- 

 tion of nerve ; for, thinking that there might possibly be some passage of 

 the current from the clay into the nerve in a semilenticular form, I tried 

 a number of times the effect of ligaturing a nerve with a fine human hair, 

 then with a fine pair of scissors making the transverse section as close 

 beneath the ligature as possible, and, lastly, lowering the nerve-section 

 on the clay as before. In no one case, however, did I succeed in ob- 

 taining any results similar to those which I obtained with unligatured 

 nerves. It may be stated that in all these experiments with the clay 

 bridge, I graduated the amount of nerve-length to be laid on it by means 

 of a horizontal glass rod firmly fixed to the tube of a microscope. The free 

 end of the rod was pointed, and usually passed between the tendo Achillis 

 and the tibia, the latter having been previously severed at the knee. 

 The sciatic nerve was thus allowed to depend in a vertical direction, and 

 could be very accurately adjusted upon the clay bridge by means of the 

 rack-work which moved the tube of the microscope. 



§ 6. During the course of the above investigation concerning the 

 effects of nerve-injury on excitability, several other facts of interest were 

 incidentally observed. It seems desirable, therefore, to add a brief 

 account of these facts. 



When an uncurarized muscle is in a state of moderately strong tetanus 

 from the passage of a rather weak galvanic current, it may occasionally 

 be observed that some part or parts of the muscle begin to jpulsate in a 

 strictly rhythmical manner — the parts concerned alternating their periods 

 of teta,nus with periods of repose, sometimes at about the rate which is 

 observable in a frog's lymphatic heart, and sometimes faster. I have 

 daunted such pulsations through more than 100 revolutions, without a 

 single intermission and in perfectly regular time throughout. That this 

 interesting phenomenon is exclusively due to the intramuscular nervous 

 element is, I think, proved by the fact that I have never seen it to occur 

 in any one of the hundreds of curarized muscles which I have this year 

 subjected to the influence of the constant current. Moreover, on one 

 occasion I noticed a very good instance of rhythmical pulsation in a 

 partly tetanized gastrocnemius, when I happened to have the attached 

 sciatic on another pair of electrodes. Of course it occurred to me to try 

 the effects of throwing the nerve near the muscle first into anelectro- 

 tonus and then into kathelectrotonus. The results were most decided. 

 With a current of properly graduated intensity passing through the 

 gastrocnemius, it was always quite easy to inhibit the pulsating effect in 

 the muscle by throwing the attached nerve into anelectrotonus, while 

 the pulsations were always seen to recommence as soon as the polarizing 



