ENERGY AND RAPIDITY OF MUSCULAR CONTRACTION. 919 



muscular contraction to the movement of the body, is very commonly disad- 

 vantageous as regards force ; being designed to cause the part moved to pass 

 over a much greater space than that through which the muscle contracts. Thus 

 the Temporal muscle is attached to the lower jaw, at about one-third of the dis- 

 tance between the condyle and the incisors ; so that a shortening of the muscle 

 to the amount of half an inch will draw up the front of the jaw through an 

 inch and a half; but a power of 900 Ibs. applied by the muscle would be 

 required to raise 300 Ibs. bearing on the incisors. In the case of the forearm 

 and leg, the disproportion is much greater ; the points of attachment of the 

 muscles, by which the knee and elbow-joints are flexed and extended, being 

 much closer to the fulcrum, in comparison with the distance of the points on 

 which the resistance bears. 



922. The rapidity of the changes of position of the component particles of 

 muscular fibres may, as Dr. Alison justly remarks, 1 be estimated, though it 

 can hardly be conceived, from various well-known facts. The pulsations of the 

 heart can sometimes be distinctly numbered in children, at more than 200 in 

 the minute ; and as each contraction of the ventricles occupies only one-third of 

 the time of the whole pulsation, it must be accomplished in l-600th of a minute, 

 or 1-1 Oth of a second. Again, it is certain that, by the movements of the tongue 

 and other organs of speech, 1500 letters can be distinctly pronounced by some 

 persons in a minute ; each of these must require a separate contraction of mus- 

 cular fibres ; and the production and cessation of each of the sounds imply that 

 each separate contraction must be followed by a relaxation of equal length; each 

 contraction, therefore, must have been effected in l-3000th part of a minute, or 

 in 150th of a second. Haller calculated that, in the limbs of a dog at full speed, 

 muscular contractions must take place in less than the l-200th of a second, for 

 many minutes at least in succession. All these instances, however, are thrown 

 into the shade, by those which may be drawn from the class of Insects. The 

 rapidity of the vibrations of the wings may be estimated from the musical tone 

 which they produce ; it being easily ascertained by experiments, what number 

 of vibrations are required to produce any note in the scale ( 908). From these 

 data, it appears to be the necessary result, that the wings of many Insects strike 

 the air many hundred, or even many thousand, times in every second. The 

 minute precision with which the degree of muscular contraction can be adapted 

 to the designed effect, is in no instance more remarkable than in the Glottis. 

 The musical pitch of the tones produced by it is regulated by the degree of 

 tension of the chordae vocoles, which are possessed of a very considerable degree 

 of elasticity ( 928). According to the observations of Miiller, 2 the average 

 length of these, in the male, in a state of repose, is about 73-100ths of an inch; 

 whilst, in the state of greatest tension it is about 93-100ths; the difference being 

 therefore 20-100ths, or one-fifth of an inch : in the female glottis, the average 

 dimensions are about 51-100ths, and 63-100ths respectively; the difference being 

 thus about one-eighth of an inch. Now the natural compass of the voice, in 

 most persons who have cultivated the vocal organ, may be stated at about two 

 octaves, or 24 semitones. Within each semitone, a singer of ordinary capability 

 could produce at least ten distinct intervals ; so that of the total number, 240 is 

 a very moderate estimate. There must, therefore, be at least 240 different states 

 of tension of the vocal cords, every one of which is producible by the will, with- 

 out any previous trial ; and the whole variation in the length of the cords being 

 not more than one-fifth of an inch even in man, the variation required to pass 

 from one interval to another will not be more than l-1200th of an inch. And 



1 " Cyclopaedia of Anatomy and Physiology," Art. "Contractility." 



2 "Elements of Physiology," Baly's translation, p. 1018. 



