CONTRACTION AND WORK OF THE MUSCLES. 43 



point of the nerve very near to the muscle, he ascertained 

 that under these new conditions the motion followed the ex- 

 citement more closely. The difference of time which he 

 observed in these two consecutive experiments measured the 

 duration of the transference of the nervous agent along the 

 known length of the nerve, and consequently expressed its 

 speed, which varied from 15 to 30 metres per second. It 

 is feebler in the frog than in warm-blooded animals. 



Fig. 10.- -Determination of the speed of the nervous agent in man. 1. Shock 

 produced when the nerve has been excited very close to the muscle. 

 2. Shock produced by the excitement of the nerve at a farther distance 

 of 30 centimetres. D, Vib ation of a chronograpbic tuning-fork vibrating 

 250 time=! in a second, servjng to measure the time which corresponds with 

 the interval of the shocks. 



Now, it results from the experiments of Helmholtz, that all 

 the time which elapses between the excitement and the motion 

 is not occupied by the transference of the nervous agent ; but 

 that the muscle, when it has received the order carried by the 

 nerve, remains an instant before acting. This is what Helm- 

 holtz calls lost time. This time would correspond, in the 

 comparison which we have employed above, with the duration 

 of the preparatory labour between the arrival of the letters 

 and their distribution. 



Physiologists have repeated the experiment of Helmholtz 

 with some improvements. In fig. 10 tracings may be seen 

 which we have ourselves obtained while measuring the speed 

 of the nervous agent. 



Two muscular shocks are successively registered upon the 

 same cylinder, care being taken that the nerve shall be excited 

 in the two experiments, at different points, but at the same 

 instant with regard to the rotation of the cylinder; for 

 example, at the precise moment at which the point of the 



