GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 91 



slower; the nerve for the claw-muscles of the lobster conducts at a rate of 

 from 6 to 12 meters per second, according as the temperature is low or high 

 (Fredericq and Vandervelde). The rati' in non-medullated nerves of the 

 Cephalopodia is 3.5-5.5 meters per second | Boruttau). 



Contrary to the view frequently expressed (Pfliiger 1 and others), all parts 

 of the nerve have the same rate of conduction. 2 



Rate in Sensory Ni roes. — We have no definite knowledge of the rate of 

 conduction in sensory uerves. The attempt lias been made to measure it by 

 stimulating the sensory fibres of a nerve-trunk at two different points and 

 noting the difference in the time of the beginning of the resulting reflex acts ; 

 or, in experiments on men, the difference in the length of the reaction time 

 has been taken as an indication. By reaction time is meant the interval 

 which elapses between the moment that the irritant is applied and the signal 

 which is made by the subject as soon as he feels the sensation. Oehl found 

 the mean normal rate of conduction in the sensory nerves of men to be 36.6 

 meters per second. 3 Dolley and Cattell, 4 by employing the reaction-time 

 method, found the rate for the sensory fibres of the median nerve of one of 

 them to be 21.1 meters per second, and for the other 49.5 meters per second, 

 while the posterior tibial nerve gave rates, for one of them 31.2 meters, and 

 for the other 64.9 meters. They attribute these wide variations in part to 

 differences in the effectiveness of the irritant at different parts of the skin, 

 but chiefly to differences in the activity of the central nervous processes 

 involved in the act. 



Schelske ' observed similar differences in different men — for one 25.3 

 meters, for another 32.6 meters, and for still another 31.05 meters per 

 second. 



In spite of the great difficulty of getting definite measurements in experi- 

 ments on men, we may conclude from the work of these and other observers 

 that the rate of conduction in sensory fibres is about the same as in motor 

 fibres; in the case of man about 35 meters per second. 



Another method applicable to isolated nerves is based on the fact that the 

 passage of the nerve-impulse along a nerve is accompanied by a change in 

 its electrical condition. The rate of conduction can be ascertained by finding 

 the rate at which this electrical change is transmitted. 



Influences which Alter the Rate and Strength of the Conduction-proc- 

 ess. — (a) Effect of Death-processes. — Normally, the rate of conduction in mus- 

 cle-fibres is SO rapid that the whole muscle appears to contracl at the same time ; 

 but there are certain conditions under which the transmission of the exciting 

 influence is very much slowed, <>r even altogether prevented, so that the stimu- 

 lation of a given part of the muscle results in a local swelling, or welt, limited 



1 Pfliiger: Uhtersuchungen itber die Physiologic da ElectrotoTvua, Berlin, 1859, S. 465. 

 J R. du Rois-Reymon.l : CentralblcUtfur Physiologic, 1899, Bd. xiii. S. 513. 

 3 ()ehl : Archives italiennes de Biologic, 189"), xxi. .'>, p. 401. 



*Dollc-y and ('attell : Psychological Review, New York and London, 1 894, i. p. 159. 

 'Schelske: Archiv fur Anatomic uml Plu/sinlniiir, lStil, S. 151 . 



