24 PHYSIOLOGY CHAP. 



greater part of the duration of the wave, each segment of the 

 fibre will be in some phase of activity, which is more advanced in 

 the segments nearer to, less advanced in those more distant from, 

 the points at which the stimulus is applied. 



The rate of propagation varies considerably in the muscles of 

 the same animal according to the method adopted. According to 

 Aeby (I860), who first applied the graphic method to this research 

 in the gracilis and semi-membranosus muscles of the frog, it is 

 about 1 m. per second (1-2-1-6 m.). Von Bezold's and Marey's 

 results were much the same, while Bernstein, who compared the 

 moments at which successive waves, travelling in the same 

 direction from different points, reached a particular spot at a 

 known distance from each of them, obtained much higher values 

 (3 -2-4-4 m. per second). Hermann who excited the two sartorius 

 muscles in a curarised frog at two different points, and simultane- 

 ously, gave the rate as 2'7 m. per second. 



Just as the velocity of the muscle twitch differs considerably 

 in the muscles of different animals (cold-blooded and warm- 

 blooded), and in different muscles (pale or red, quick or torpid), so 

 the velocity at which the wave of excitation or contraction travels 

 also varies. In the retractor collis muscle of the tortoise the rate 

 at which excitation is transmitted varies between 0'5 and 1'8 m. 

 (Hermann and Aeby) ; while in the sterno-mastoid muscle of the 

 dog it is equal to 3-6 m. (Bernstein and Steiner). 



The rate of propagation of the wave may v.iry greatly in the 

 same muscle with the strength of stimulus, still more with the 

 state of its excitability, which varies largely according to fatigue 

 and with the temperature. Schiff (1856-58) first studied the 

 interesting phenomenon known as the ideo-muscular contraction, 

 which directly shows the transmission of a contraction excited by 

 mechanical stimuli along mammalian muscles exposed shortly 

 after death. A ridge or weal forms when the muscle is tapped 

 or stroked with a blunt object, and persists for a certain time ; 

 two contractile waves start from it, and spread towards the 

 two ends of the muscle, where they are reflected back towards 

 the spot stimulated, and collide with secondary waves from the 

 weal. As the excitability of the tissue is exhausted, the velocity 

 of this wave conduction also diminishes. 



These observations on the propagation of the contraction wave 

 through the muscle refer to artificial direct stimulation at one 

 end. With natural or indirect stimuli, when the excitation 

 reaches the muscle through the end-plates of the motor nerves that 

 lie towards the middle of each fibre, the contraction must invade 

 the total length of the fibres in a much shorter time. In fact we 

 assume that the contraction is propagated from the end-plates in 

 two opposite directions towards the two ends of the fibres, and 

 therefore has only to traverse half its length. 



