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sartorius, the muscle responds by a lower frecjuency if the stimuli are 

 weak [(4), pi. vi., ph. 80 and 81]. Experiments made soon afterwards (in 

 1902), but of which no account has yet been published, showed what I was 

 then not expecting, namely, that when stimuli of a frequency so great as to 

 be incapable of impressing itself upon the muscle were applied to the nerve, 

 however nuich their strength was reduced, the response frequency was not 

 reduced ; that is to say, although the response frequency differs in different 

 records, as it always does when it bears no relation to the exciting fre- 

 quency, it does not vary with the strength of the stimulus. Fig. (S A 

 is a record of the response of a sartorius muscle the nerve of which 

 was excited by the vibrations of a 500 fork acting upon a telephone 

 transmitter, with a whole Daniell in the primary circuit of the telephone 

 transmitter. The undulations are seen to recur Avith a frequenc}^ of about 



Fig. 8. — Electrical response of frog's sartorius to excitation of the nerve by currents of high 

 freijuencj^ (to a tuning fork giving 500 d.v. per second, sounded in front of a telephone trans- 

 mitter). Recording surface describing an arc. Rate of movement indicated by a 500 fork. 

 A, a whole Daniell in primary circuit. B, only a third of a Daniell in primary circuit. 



88 per second. Fig. 8 B is the record obtained when only one-third of 

 the Daniell was in the primary circuit. The muscle gave a much smaller 

 contraction, and all four times that the electrical response was recorded 

 with the strength of the stimulus so much reduced, it began, as in the 

 record reproduced, a much longer time after the currents began to act 

 on the nerve, i.e. after the break of a short circuit by the signal s. 

 When the response began, however, the undulations had always a fre- 

 quency as great as in any of the records taken with a stronger stimulus. 

 In all four it was about 100 per second, whereas in the eleven records 

 which were taken with the stimulus stronger the frequency varied between 

 65 and 100 per second. A stimulus therefore, which may be regarded as 

 a continuous one may produce the same rhythm in muscle whatever its 

 strength, whereas a series of stimuli of a frequency low enough for the 

 muscle to follow, as one of 50 per second would be, and is, may fail to 

 be all of them effectual when their strenofth is reduced. 



