330 PROTOPLASMIC ACTION AND NERVOUS ACTION 



of the local bioelectric variations, as related to the 

 transmission-velocity of the excitation-wave in a variety 

 of vertebrate and invertebrate tissues under different 

 conditions. It will be noted that cold, anaesthesia, and 

 fatigue, which retard the rise of the bioelectric variation, 

 also retard the speed of propagation in about the same 

 proportion. The general correspondence shown seems 

 to leave no doubt that a direct correlation exists between 

 the respective rates of development of the local electric 

 processes and the velocities with which excitation is 

 transmitted from region to region in the different 

 conducting tissues. 



This fact, taken by itself, may seem equivocal in its 

 significance, since it is evident that any wave of alteration 

 occupying a definite length of the conducting element 

 and associated with a change of potential would, as it 

 passed one of the electrodes of a recording instrument 

 (e.g., a string galvanometer), cause an excursion, the 

 rate and duration of which would depend on the speed 

 of the wave. The electric variation might thus con- 

 ceivably be simply a sign or index of the passage of a 

 wave of activation, without having any causal relation 

 to the process of transmission. Other evidence, however, 

 to be considered below, indicates that the electric 

 variation, as such, is the main factor determining the 

 transmission of excitation from the active region to the 

 adjoining resting region (see chap. xv). 



It is significant that many normal bioelectric 

 processes, e.g., those accompanying muscular contraction 

 or nervous activity, as they occur under physiological 

 conditions in the intact organism, are typically rhythmi- 

 cal. The underlying chemical reactions must therefore 



