428 NERVOUS IRRITABILITY 



stimulated at the wrist, at the elbow, and at the upper arm near the 

 lower extremities of the coraco-brachialis and deltoid muscles ; the effect 

 of the stimulation being marked by the swelling of the muscles at the 

 ball of the thumb. Here also it was found that the intervening time 

 between the application of the electrodes and the muscular contraction 

 was greater when the stimulus was applied to the nerve at the upper 

 arm, than when applied at the wrist ; this increased interval being evi- 

 dently the time required for the transmission of the nervous impulse 

 from one point to the other. The rate of transmission, as ascertained 

 by these experiments, was found to vary considerably according to the 

 different conditions of cold and warmth; the transmission in the me- 

 dian nerve, when subjected to cold, being sometimes less than one-half 

 as rapid as in the same nerve at a higher temperature. 



Finally, in the experiments of Burckhardt, 1 the rate of transmission of 

 the nerve force, for voluntary motion and the acts of conscious sensa- 

 tion in man, has been investigated at considerable length. In these 

 experiments, an automatic registering apparatus was employed, in which 

 the beginning and end of the nervous transmission were marked, as 

 above, by corresponding deviations of a traced line. 



Hate of Transmission in the Motor Nerves. The transmission of 

 the voluntary impulse was measured in Burckhardt's investigations as 

 follows : The galvanic battery and the registering apparatus being pro- 

 perly attached to the person serving for experiment, the signal for the 

 contraction of a particular muscle was given by the sound of a bell 

 connected with the battery. Thus the entire interval registered was 

 that between the sound of the bell and the muscular contraction. A 

 part of this time was consumed in the double act of hearing the sound 

 and producing the volitional impulse. A part was also taken up in the 

 local process of muscular contraction, and only the remainder was occu- 

 pied in that of nervous transmission. But it is evident that, if, in two 

 different observations, the same signal were used for the contraction of 

 two -muscles supplied by different lengths of nerve, the process taking 

 place in the brain and that taking place in the muscle would be alike 

 in both ; and any difference in the time observed must be due to the 

 different distances of nerve fibre traversed by the voluntary motor 

 impulse. The muscles employed for this purpose were, in the lower 

 limb, the extensor digitorum communis brevis, tibialis anticus, and 

 semimembranosus, supplied by branches of the sciatic nerve, and the 

 quadriceps extensor cruris, supplied by the anterior crural nerve; in 

 the upper limb, the interosseus externus primus, extensor digitorum 

 communis, flexor digitorum and deltoid, all supplied by branches of 

 the brachial plexus. The result of all the observations upon eight 

 different healthy persons was, that the mean velocity of transmission 

 for the voluntary impulse, in the peripheral nerves of the upper and 



1 Die Physiologische Diagnostik der Nervenkrankheiten. Leipzig, 187o, 

 p. 32. 



