90 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



following experiment it was stimulated near the other end. The distance 

 between the stimulated points being known, the rate of transmission was 

 reckoned from the difference in the latent periods. In his experiments he 

 found the rate of conduction in the semimembranosus of the frog to be from 

 3.2 to 4.4 meters per second. Hermann found the rate to be 2.7 meters for 

 the curarized sartorius of the frog. The results obtained by Abey and some 

 others are a little lower, but probably 3 meters per second can be accepted as 

 the average normal rate for frog's muscle. 



Length of Wave. By such experiments it becomes obvious that the con- 

 traction process passes over the muscle, in the form of a wave. In an experi- 

 ment, such as Bernstein's, in which the thickening of the muscle is recorded, 

 we can determine from the length of the curve written by the contracting 

 muscle how long the contraction remains at a given place. Knowing this, 

 and the rate at which the process passes along the fibre, we can estimate the 

 length of the contraction wave, just as we could reckon the length of a train 

 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 at 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 (Waller). 



Contractile substance of medusse 0.5 (Waller). 



Neck-muscles of the turtle O.'l -0.5 (Hermann and Abey). 



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



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



Sterno-mastoid of the dog 3. _ 6 (Bernstein and Steiner). 



feemimembranosus (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. The process is accompanied by no 

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



