JIG PHYSIOLOGY OF ML'SCLKS AND NERVES. 



in time and from the distance between the two irritated 



{'hits the rate of propagation of tlie excitement was 

 found to be 30 in. per second. The high figure ;is com- 

 pared \vith that found with the nerves of frogs i> 



A O 



plained l)y the higher temperature of human ner\es. 

 The rate of propagation would indeed be much lowered 

 if the temperature of the arm were considerably de- 

 creased by the use of ice. 



The above calculation of the rate of propagation is 

 made OH the assumption that this rate is constant, 

 throughout its duration. There is, however, nothing 

 to show that this is the case. On the contrary, it is 

 more probable, that the propagation proceeds at first at 

 a greater and afterwards at a less speed. This may be 

 infern-d from an experiment arranged by H. IMunk. If 

 three pairs of wires are applied to a long nerve, one 

 close to the, muscle, another at the centre, and the 

 third considerably above, and then causing three con- 

 secutive curves to describe themselves on the mvo- 

 graph plate by irritating these three points, it will 

 be found that the three curves are not equally removed 

 from each other; on the contrary, the first and second 

 stand very near together, while the third is far from 

 the two former. More than double the time was re- 

 quired for the excitement to traverse the full distance 

 from the upper to the lower end than it took to traverse 

 the half-distance from the middle of the nerve to its 

 louer end. The simplest explanation which can be 



given of this phenomenon is that t he excitement during 



its propagation is gradual ly retarded, just as a billiard ball 

 moves al tirst very quickly bill afterward at a gradually 

 decreasing speed. The retardation of the billiard ball 

 is due to the friction of (he undcrl \ ing surface. From 



