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ANNALS NEW YORK ACADEMY OF SCIENCES 



parallelism between the range of frequencies in the local rhythmic re- 

 sponse, the fundamental frequency in the trains of chemically initiated 

 impulses, and the undamped natural frequency of the resting nerve 

 membrane, support Cole's suggestion^* that it is the structural charac- 

 teristics of the membrane which govern the periodic activity of nerve. 



Two frequencies of nerve action have been described in the foregoing 

 discussions of the response of nerve to chemical excitation. One is the 

 average number of impulses conducted along the nerve per second; the 

 other is the fundamental and relatively constant frequency of the 

 excitatory process, which has, in the case of squid nerve, been identi- 

 fied with the local electric response. 



Solutions are modified sea water. Cal- 

 cium and magnesium omitted in B and C. 

 Magnesium omitted in A. KCl concen- 

 tration and pH are same as in sea water. 



Figure 22. Values for the fundamental frequency obsei-ved in 10 giant axons of the squid (Loligo 

 pealii), estimated from frequency of conducted impulses. Stimulation by topical application of in- 

 dicated isotonic solutions. 



The relation between these two frequencies is illustrated by the fol- 

 lowing experiment, which makes use of the fact that a polarizing cur- 

 rent may modify the average frequency of impulses discharged from a 

 calcium-deficient region of nerve. In figure 13, the outward flow of 

 current across the chemically altered nerve membrane caused a tran- 

 sient increase of the average impulse frequency. The distribution plot 

 for the intervals between impulses from the non-polarized nerve is 

 shown in the lower half of figure 23. The intervals between some im- 

 pulses were 3.2 milliseconds; other impulses recurred at intervals which 

 were about two times this value. 



In accordance with the concepts which have been developed in this 

 section, we may say that there was a rhythmic excitatory process, in the 

 chemically modified portion of the nerve, of a fairly constant frequency. 



