RAPIDITY OF NERVOUS CONDUCTION 481 



on the paper, moving at the same rate, the instant when contraction 

 takes place, it is evident that the interval between two contractions 

 produced by stimulating the nerve at different points in its course may 

 be accurately measured ; and if the length of the nerve between the two 

 points of stimulation is known, the difference in time will represent the 

 rate of nervous conduction. In experiments on frogs the leg is prepared 

 by cutting away the muscles and bone of the thigh, leaving the nerve 

 attached. The lever is then applied to the muscles of the leg, and the 

 nerve is stimulated successively at two points, the distance between 

 them being measured. 



Employing the myograph of Marey, Baxt, in the laboratory of Helm- 

 holtz, succeeded in measuring the rate of nervous conduction in the 

 human subject. In these experiments, the swelling of the muscle dur- 

 ing contraction was limited by enclosing the arm in a plaster-mould, and 

 the contraction was observed through a small opening. By then excit- 

 ing the contraction by stimulating the radial nerve successively at dif- 

 ferent distances from the muscle, the estimate was made. The rate in 

 the human subject was thus estimated at one hundred and eleven feet 

 (33.9 meters) per second. 



The method used in determining the rate of conduction in motor 

 nerves an estimation of the difference in time of the passage of a 

 stimulus applied to a nerve at two points situated at a known distance 

 from each other has been applied to the conduction of sensations. 

 Hirsch made the first attempt to solve this question, in 1861. He 

 employed the delicate chronometric instruments used in astronomy and 

 noted the difference in time between the appreciation of an impression 

 made on a part of the body far removed from the brain, as the toe, 

 and an impression made on the cheek. This process admitted of a 

 rough estimate of about one hundred and eleven feet (33.9 meters) per 

 second as the rate of sensory conduction. 



It is not necessary to describe fully the apparatus by means of 

 which the most recent estimates of the rate of nervous conduction have 

 been made. The general results of the observations of Helmholtz, Marey, 

 Baxt, Schleske and of many others nearly correspond with the estimates 

 just given, and they show that the rate is about the same for motor and 

 sensory nerves. This rate is modified by various conditions. It is 

 diminished in the anelectrotonic and increased in the catelectrotonic 

 condition of nerves. In the frog Helmholtz observed that the rate was 

 much reduced by cold ; at 32 Fahr. (o C.) being not more than one- 

 tenth as rapid as at 60 or 70 Fahr. (15.5 or 21.11 C.). 



The rate of transmission of impulses and impressions through the 

 spinal cord has been investigated by calculating the distances between 



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