294 OF MUSCULAR CONTRACTILITY. 



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 ff | th 

 of a minute, or T Vth of a second. Again, it is certain that, by the movements 

 of the tongue and other organs of speech, 1500 letters can be distinctly pro- 

 nounced 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, implies that each separate contraction must be followed by a 

 relaxation of equal length ; each contraction, therefore, must have been effected 

 in Vo tn P art of a minute, or in the T \>th of a second. Haller calculated 

 that, in the limbs of a dog at full speed, muscular contractions must take place 

 in less than the o^th 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. From these data, it appears to be the neces- 

 sary 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 vocales, which are possessed of a very considerable degree of elasti- 

 city ( 402). According to the observations of Miiller,*the average length of 

 these, in the male, in a state of repose, is about /^hs f an i nc ^ 5 whilst, in 

 the state of greatest tension it is about T 9 ^o tns 5 tne difference being therefore 

 or one-fifth of an inch : in the female glottis, the average dimensions 



are about yVV tns ' anc ^ T 6 o 3 o tns respectively ; the difference being thus about 

 one-eighth of an inch. Now the natural compass of the voice, in most per- 

 sons 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 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 one-twelve 

 hundredth of an inch. And yet this estimate is much below that which 

 might be truly made from the performances of a practised vocalist.! 



398. Of the different associations of muscular actions which are employed 

 for various purposes in the living body, it would be out of place here to speak ; 

 since these associations depend upon the nervous rather than upon the mus- 

 cular system ; and the most important of them have already been considered 

 in detail. It may be mentioned, however, that the aptitude which is acquired 

 by practice, for the performance of particular actions, that were at first ac- 

 complished with difficulty, seems to result as much from a change, which the 

 continual repetition of them occasions in the muscle, as in the habit which the 

 nervous system acquires, of exciting their performance. Thus almost every 



* Physiology, p. 1018. 



f It is said that the celebrated Mad. 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 

 ihe 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. 



