GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 89 



of cars if we knew how fast it was moving and how long; it required to pass 

 a given station. Thus, if the contraction is found to last al a given point 

 on the muscle 0.1 second, and the rate at which the contraction process is 

 travelling is 3000 millimeters per second, the length of the wave is 300 milli- 

 meters. According to Bernstein's determinations, the length of the wave of 

 contraction in a frog's striated muscle is from 198-380 millimeters. The 

 length of a striated muscle-fibre is, at the most, scarcely more than 40 milli- 

 meters, and normally the muscle-fibre is stimulated, not as in the above ex- 

 periment at one end, but near its centre, at the point where the nerve joins 

 it; the irritation process spreads along the fibre in both directions from this 

 point, and would pass over the distance 20 millimeters so quickly that practi- 

 cally the whole muscle-fibre would be in the same phase of contraction at the 

 same time. 



Rate of Conduction in Different Kinds of Muscle. — The rate of conduction 

 varies very considerably in the muscles of different animals, and in different 

 kinds of muscle in the same animal, just as the contraction process itself dif- 

 fers in its rate and strength. 



Meters per second. 



Smooth muscle-fibres of the ureters of the rabbit . . . 0.02-0.03 (Engelmann). 



Muscle of the heart-ventricle of the frog 0.1 I Waller). 



Contractile substance of medusa; 0.5 (Waller). 



Neck-muscles of the turtle 0.1 -0.5 ( Hermann and Abey). 



Gracilis and semimembranosus of the frog .... 3.2 -4.4 (Bernstein). 



Cruralis (red muscle) of the rabbit 3.4 (Rollet). 



Sterno-mastoid of the dog 3. -6 (Bernstein and SteinerV 



Semimembranosus (white muscle) of the rabbit . . . 5.4-11.4 (Rollet). 



Human muscle 10. -13 (Hermann). 



(b) Rate of Conduction in Nerves. — Conductivity is most highly developed 

 in the case of the nerve-fibre. The distances through which it acts and the 

 rapidity of the process excite our wonder, 'flic process is accompanied by no 

 visible change in the nerve-fibre itself, and the strength and rate have to be 

 estimated by the effect produced on the organ which the nerve excites to action, 

 or by the change which takes place in the electrical condition of the nerve as 

 the wave of excitation sweeps over it. 



Rate in Motor Nerves. — Helmholtz was the first to measure the rate of con- 

 duction in nerves. 1 Originally he employed Pouillefs method for measuring 

 short intervals of time. The arrangement is illustrated in Figure 35. The 

 moment that a current was thrown into the coils of a galvanometer (see p. 

 145) the current in the primary coil of an induction apparatus was broken 

 and the nerve connected with the secondary coil received a shork. An instant 

 after the contraction of the muscle which resulted from the stimulation of the 

 nerve broke the galvanometer circuit. The amount of deviation of the magnet 

 of the galvanometer varied with the time that the circuit remained closed, and 

 therefore could be taken as a measure of the interval elapsing between the 

 stimulation of the nerve and the contraction of the muscle. The nerve was 

 1 Helmholtz: Archivfiir Anatomie und Physioloyu; 1850, S. 71-27U; 1852, S. 199. 



