156 



When fibres, which are perfectly relaxed (but not stretched j, are measured, 

 we obtain the following data : — 



40 

 Proq muscle: Distance between striations = — fx; breadth of fibre = 30 /x. 



13 



8 



Human muscle: Distance between striations = — /x; breadth of fibre = 68 /a. 



3 



If d is the diameter of a fibre, l the distance between each successive stria- 

 tion, then the average distance that the impulses will travel in a single turn of 

 the double helicoid will obviously be given by the following formula: — 



7r2d2+(2L)2+2L 



Actual distance = \ 



2 



TT d + 2 L 



Since L is very small compared with d, we may write, actual distance= , 



approximately. 2 



Since the component of this distance along the fibre is 2 l (double helicoid), 



TT d+2 L 



the velocitv of the excitatory impulse along the spiral will be [ X longi- 



4l 

 tudinal component of the velocity], ivhere the longitudinal component is only 

 approximately known. 



If we substitute numerical values for tt, d. l, and the longitudinal com- 

 ponent, we obtain: Velocity of muscle impulse in man=133 metres per second 

 (approx. ). Velocity of muscle impulse in frog=:between 22 and 30^ metres 

 per second. 



It should be noted that the values are only approximate. The velocity of 

 the muscle wave is by no means accurately known, and everv error in 

 this will be increased 8 or 20 times in the final result. 



Now the measurements of the velocity of the nerve impulse in man show 

 this to be about 123 metres per second (Piper); that of the frog 27 metres 

 (Helmholtz). 



So closely do these results approximate to the calculated values for the 

 velocity of the excitatory impulse along the spiral, that we may say, with con- 

 siderable confidence, that the velocity of the excitatory impulse along the spiral 

 Krause's membrane, is equal to that of the nerve impulse. 



Summary. 



(1) The excitatory impulse travels through the fibre along the spiral 

 Krause's membrane. 



(2) It travels along this membrane with the velocity of a nerve impulse 

 (frog and man). 



References. 



(1921) Fulton, J. F., Amer. Jour, of Physiol., vol. 57, p. 153. 



(1922) Tiegs, Trans. Roy. Soc. S. Austr., vol. xlvi.. p. 222. 



(1923) Tiegs, ibid., vol. xlvii.. p. 142. 



