146 PHYSIOLOGY OF MUSCLES AND NERVES. 



adapted for exciting this motion than is slow action. 

 That even slight mechanical distiu'bances are capable 

 of producing excitement, although the nerve is not 

 crushed, has been proved by Heidenhain. He attached 

 a small ivory hammer to the instrument which we have 

 already described under the name of Wagner's hammer, 

 and, having laid the nerve on a small ivory anvil, 

 placed the latter under the hammer in such a way 

 that the latter tapped gently on the nerve. The result 

 of this was strong tetanus lasting for several seconds. 

 To obtain a more accurate conception of the mechanism 

 of nervous excitement, it would be necessary first to 

 learn accurately the arrangement of the smallest par- 

 ticles in the quiescent nerve. Now we shall later on 

 examine certain behaviour of the quiescent nerve from 

 which conclusions may be drawn as to the regular 

 arrangement of the smallest particles. While postpon- 

 ing the closer examination of these details, we may at 

 present try to explain the flicts of excitement as clearly 

 as circumstances permit. For this end we will assume 

 that the particles of the nerve are retained in an en- 

 tirely definite relative po>ition by molecidar forces. 

 P'xcitement can, accordingly, only intervene when the 

 particles are displaced from this position and are set in 

 motion. The more powerful are the forces which retain 

 the particles in their balanced position, the greater 

 must be the forces which move tliem, and, therefore, 

 the smaller is the excitability. It must also be ex- 

 })lained that the separate particles of the nerve mutu- 

 ally influence each other, each particle influencing the 

 olher and helping to retain it in its relative position. 

 A comparison drawn by du Bois-Reymond may be used 

 to make this somewhat involved explanation more 



