yo8 



THE CEREBRAL CORTEX. 



a rhythm of about ten or twelve contractions per second. 1 Fig. 320 

 shows such a tracing taken on a slowly moving surface, and Fig. 321 

 another tracing with the excursion more amplified and recorded upon a 

 more quickly moving paper. The rate of rhythm is very constant for 

 the same individual, but varies in different individuals (from 8 to 



13 per second), when the 

 muscle is contracting against 

 a small resistance. Accord- 

 ing to the observations of 

 W. Griffiths 2 it may be- 

 come even more rapid (15 

 or 18 per second) with 

 increase of the resistance 

 up to a certain point, and 

 then again diminish, and it 

 undergoes similar changes 

 of rate if the experiments 

 be long-continued so as to 

 produce fatigue. The vibra- 

 tion observable in the out- 

 stretched arm, when hold- 

 ing a weight, shows the 



Fio.321.-Part of a similar tracing, taken on a faster same rate f ^hythm as 

 surface and with the movements more amplified. 



the muscle 

 322). 



curve (Fig. 



Probably 10 per second may be taken as the average rate of rhythm, and 

 20 per second as the maximal rate. This would make the average interval 

 between the consecutive nervous discharges from the cortical cells 01 second, 

 and the minimal interval 0'05 second. Richet found that in shivering the 

 number of contractions per second in the muscles affected, was about 10 to 11 



FIG. 322. Vibrations of the outstretched arm holding a weight of 

 about six kilos. The tracing was recorded by the apparatus 

 shown in Fig. 319. W. Griffiths. 



per second, and did not exceed 13 per second, 3 and that it is impossible to 

 articulate at a rate of more than 11 syllables per second. That this rate 

 originates in the cells of the brain appears probable from the fact, also pointed out 

 by Richet, that it is impossible to think the act of articulation at a greater rate 



1 Schafer, Journ. PhysioL, Cambridge and London, 1885, vol. vii. p. 114 ; v. Kries, 

 7 /. PhysioL, Leipzig, 1886. 



ourn. PhysioL, Cambridge and London, 1888, vol. ix. p. 39. 



Arch.f. PhysioL, Leipzig, 1886. 



2 Journ. Physu 



3 Trav. du Jab. de Marey, 1895, tome iii. p. 17. 



