THE MUSCULAR MOTOR AND ALIMENTATION 129 



wide limits, and corresponds to different rhythms. Thus, when 

 the subject is in repose, the heart makes about 70 contractions a 

 minute, which is its proper rhythm. 



The "maximum rhythm" has been determined for several 

 organs ; the fingers beat from 8 to 9 strokes a second, that 

 is to say 480 to 540 per minute. This has been tested electrically, 

 the fingers closing a circuit at each beat when tapping a metallic 

 surface,^ 1 ) the jaw gives at most 360 contractions, the foot 

 210 flexions per minute ( 2 ) ; the great toe gives a little more 

 than the foot, about 250 strokes ( 3 ) ; the fore-arm 230 to 240 

 flexions, the leg 120 (against the thigh). 



Thus it is evident that the work of the fingers is the most rapid, 

 which is confirmed by common experience. Also it can safely 

 be said that there is a special rhythm for each muscle, or group of 

 muscles. The speed of the movements of the joints is also of 

 interest. The phalanges give at the very most 300 to 400 strokes 

 to the minute, the wrist 690, the elbow 530, the shoulder 310. 

 Thus the wrist and the elbow, in the act of writing, or in needle- 

 work, are more rapid than the shoulder, or the fingers, ( 4 ) 



These speed limits vary with age ; from 6 to 16 years they 

 vary in the ratio of 2 to 3, with a retardation between 12 and 13 

 (as in the weight and strength of the body) . 



The example of the heart, which in health beats at the rate of 

 70 beats per minute, shows that there must be an indefatigable 

 muscular rhythm, a " normal rhythm." 



The following values relate to " unloaded " muscles : 



Forearm 30 to 35. 



Masticatory muscles 90 to 100. 



Fingers ... ... ... ... ... 150 



Heart 70 



We shall see later ( 120) that the " normal rhythm " is lowered 

 when the muscles are loaded. 



People of small stature are "relatively" stronger than tall 

 ones, and quicker, because weight decreases as the cube of the 

 size, whilst "force" only decreases as the square being propor- 

 tional to the section of the muscle (see next para.). Borelli said : 

 " Quo minora sunt animalia eo ma j ores faciunt saltus," ( 5 ) An 

 interesting example ( 6 ) of the variation of the normal rhythm 

 inversely to the stature is that of the muscles of mastication. 



(!) Von Kries (Arch.f. Anat. u. Physiol., Suppl. B., 1886, p. 6)) ; Dresslar 

 (Amer. Jl. of Physiol., vol. iv., p. 514, 1892) ; Bryan (ibid., v., p. 123). 



( 2 ) Von Kries (loc. cit.). 



( 3 ) Davis (Studies from the Yale Psychol. Lab., vol. vi., p. 11, 1898). 

 () Bryan (Amer. Journ. of Psych., iv., 514, 1892). 



( 6 ) Borelli, De Motu Animalium, 1710, Leyden, edn., p. 181. 



( 6 ) V. Ducceschi (Verworris Zeitsch. f. Allg. Physiol., vol.ii.,p. 482, 1903). 



