100 NERVOUS SYSTEM. 



propagation through immense space, as we ha V T C in the case 

 of light." 1 



The conjectures of writers before Haller were based upon 

 the supposed similarity between nervous conduction and the 

 passage of electricity ; but Haller formed an estimate of the 

 rapidity of nervous conduction by ascertaining the number 

 of letters he was able to pronounce in one minute in read- 

 ing aloud from the " JSneid." a Calculating then the dis- 

 tance of the nervous course from the brain to the muscles, 

 he estimated that the nerve-force moved at the rate of about 

 one hundred and fifty feet in a second. 3 This estimate is 

 not very far from the truth ; at all events, it gives an idea 

 of the relative slowness of nerve-conduction as compared 

 with electricity or light, which travels at the rate of many 

 hundred millions of feet in a second. 



The first rigorous estimates of the velocity of the nerve- 

 current were made in 1850, by Helmholtz, 4 and were applied 

 to the motor nerves. The important and interesting re- 

 sults of these experiments were arrived at by an ingenious 

 application of the graphic method, which has since been so 

 largely improved and extended by Marey, and their accuracy 

 was rendered possible by the exceedingly delicate chrono- 

 metric apparatus which has been devised within the last 

 few years. 



It is unnecessary to describe fully the exact methods 

 employed by Helmholtz and those who immediately followed 

 in his investigations ; suffice it to say that this distinguished 

 physiologist and physicist constructed apparatus which, 

 though somewhat complex, was so accurate as to leave no 

 doubt as to the reliability of his results. Taking into 

 account all of the disturbing conditions, and allowing for the 



1 MULLER, Elements of Physiology, London, 1840, vol. i., p. 729. 



* HALLER, Elementa Physiologice, Lausannse, tomus iv., p. 483. 



8 Op. tit., tomus iv., p. 373. 



4 HELMHOLTZ, Note sur la vitesse de propagation de Tagent nerveux dans les 

 nerfs rachidiem. Comptes rendus, Paris, 1850, tome xxx., p. 204, and, 1851, 

 tome xxxiii., p. 262. 



