130 THE PHYSIOLOGY OF NERVE 



which the impulse requires for its journey through this particular 

 stretch of nerve. 



The values which Helmholtz obtained varied between 24.6 and 

 38.4 m. in a second, the determinations being made at temperatures 

 varying between 11 and 21 C. At the average temperature of the 

 room, the velocity for the musculo-motor nerves of the frog may there- 

 fore be said to be about 28 m. in a second. By recording the contrac- 

 tions of the muscles of the thumb during stimulation of the median 

 nerve at two widely separated points, Helmholtz and Baxt 1 have also 

 determined the speed of conduction in human nerves. They found it 

 to be about 34 m. in a second. In the lower animals, the rate of con- 

 duction varies considerably and even in different nerves of the same 

 animal. Fredericq and Vandervelde, 2 for example, give the value of 

 6 to 12 m. in a second for the nerve of the claw of the sea-crab, and v. 

 Uxkiill, 3 the value of 0.4 to 1 m. in a second for the nerve of the mantle 

 of cephalopods. In the nerve plexus of the heart of Limulus, Carl- 

 son 4 found the speed to be 0.4 m. in a second and in the pedal nerve 

 of Limax 1.25 m. in a second. The non-medullated olfactory nerve of 

 the pike conducts at the rate of 0.6 to 0.9 m. in a second. 5 According 

 to Chauveau, 6 the vagus fibers innervating the smooth musculature of 

 the esophagus of mammals, conduct with a velocity of 8.2 m. in a 

 second and those innervating the striated musculature of the larynx, 

 at the rate of 66.7 m. in a second. The non-medullated fibers, there- 

 fore, conduct less rapidly than the medullated; moreover, conduction 

 through the central nervous system is effected at a slower rate than 

 through the peripheral nerves. It must also be evident that the 

 speed of the wave of excitation in nerve is much less than that of 

 certain physical energies. Thus, sound travels with a velocity of 

 332 m. in a second, whereas light attains a speed of 332 million meters 

 and electricity a speed of 464 million meters per second. 



In recent years additional light has been thrown upon this topic 

 by the use of the string galvanometer. It may be stated at this 

 time that the passage of the wave of excitation is associated with an 

 electrical variation which may be accurately followed by a quickly 

 reacting galvanometer. Piper 7 employed the median nerve which he 

 stimulated either at the elbow or in the axilla. The precise moment of 

 entrance of the excitation into the distant muscles was indicated by a 

 string galvanometer adjusted in such a way that it registered the initial 

 phase of the action current in these muscles. Knowing the length of 

 the stretch of nerve intervening between the axilla and the elbow, and 

 also the time elapsing between the moment of the application of the 



1 Monatsb. der Berliner AkacL, 1870. 



2 Bull, de 1'acad. de Belgique, C. r., 1875, 91. 

 8 Zeitschr. f iir Biologic, xxx, 1894, 550. 



4 Am. Jour, of Physiol., xiii, 1905, 217. 



5 Nikolai, Pfliiger's Archiv, Ixxxv, 1901, 65. 



6 Acad. Scienc., Ixxxvii, 1878. 



7 Pfliiger's Archiv, cxxiv, 1908, 591. 



