THE STUDY OF MUSCLE PHYSIOLOGY. 



187 



was stimulated through its nerve. Precisely the same results 

 would have followed had the muscle been caused to contract by 

 the momentary application of a chemical, thermal, or mechanical 

 stimulus. 



If the length of nerve between the point of stimulation and 

 the muscle was considerable, some difference would be observed 



Fig, 175. — Diagrammatic representation of the measurement of velocity of nervous 

 Impulse (Poster). Tracms taken by pendulum myograph (Pig. 173). The nerve 

 of same muscle-nerve preparation is stimulated in one case as far as possible from 

 muscle, in the other as near to it as possible. Latent period is dd, ah\ respect- 

 ively. Difference between a6 and ah' indicates, of course, length of time occu- 

 pied by nervous impulse in traveling along nerve from distant to near point. 



in the latent period if in a second case the nerve were stimu- 

 lated, say, close to the muscle. This is represented in Fig. 175, 

 in which it is seen that the latent period in the latter case is 

 shortened by the distance from V to 6, which must be owing 

 to the time required for those molecular changes which, occur- 

 ring in a nerve, give rise to a contraction in the muscle to which 

 it belongs ; in fact, we have in this method the means of estimat- 

 ing the rate at which these changes pass along the nerve — in 

 other words we have a means of measuring the speed of the 

 propagation of a nervous impulse. The estimated rate is for the 

 frog twenty-eight metres per second, and for man about thirty- 

 three metres. As the latter has been estimated for the nerve, 

 with its muscle in ijosition in the livuig body, it must be re- 

 garded rather as a close approximation than as exact as the 

 other measurements referred to in this chapter. 



It will be borne in mind that the numbers given as repre- 

 senting the relative duration of the events vary with the ani- 

 mal, the kind of muscle, and a variety of conditions affecting 

 the same animal. 



TETANIC OONTRAOTION. 



It is well known that a weight may be held by the out- 

 stretched arm with apparently perfect steadiness for a few 



