454 OF MUSCULAR CONTRACTILITY. 



a weight equal to at least 500 times that of its body. And a small Carabus 

 has been seen to draw a weight of 85 grains (about 24 times that of its body) 

 up a plane of 25 ; and a weight of 125 grains (36 times that of its body) 

 up a plane of 5 ; and in both these instances the friction was considerable, 

 the weights being simply laid upon a piece of paper, to which the insect was 

 attached by a string. 



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

 of muscular fibres, may, as Dr. Alison justly remarks,* 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 l-10th of a second. Again, it is certain 1 that, by the move- 

 ments 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 sepa- 

 rate contraction of muscular 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 ef- 

 fected in l-1000th part of a minute, or in the l-10th 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 vibra- 

 tions of the wings may be estimated from the musical tone which they pro- 

 duce ; it being easily ascertained by experiments, what number of vibrations 

 are required to produce any note in the scale. 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 pre- 

 cision 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 ten- 

 sion of the chordx vocales, which are possessed of a very considerable de- 

 gree of elasticity ( 603). According to the observations, of Miiller,t 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 respect- 

 ively ; the difference being thus about one-eighth of an inch. Now the natu- 

 ral 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, without any previous trial ; and 

 the ivhole 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 one twelve-hundredth of an inch. And yet 

 this estimate is much below that which might be truly made from the per- 

 formances of a practised vocalist. :(: 



* Cyclopaedia of Anatomy and Physiology, Art. Contractility. 



t Physiology, 1018. 



j It is said tli:it the celebrated Made. Mara was able to sound 100 different intervals be- 

 tween each tone. The compass of her voice was at least three octaves, or 22 tones ; so that 

 the total number of intervals was 2200, all comprised within an extreme variation of one- 

 eighth of an inch ; so that it might be said that she was able to determine the contractions 

 of her vocal muscles to the seventeen-thousandth of an inch. 



