ENERGY AND RAPIDITY OF MUSCULAR CONTRACTION. 843 



increased by the passage of a continuous electrical current through the 

 nerves supplying them. 1 Thus Dr. Poore has shown that in a case where a 

 man could hold his arm outstretched for six minutes, when the current was 

 used he could go on for thirteen minutes. So also eight successive squeezes 

 of the dynamometer without galvanism gave 388 pounds, and the same 

 number with galvanism 477 pounds. Similar observations have been made 

 by Heideuhain and Remak, who have termed such currents " refreshing " or 

 " restorative." 



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

 muscular fibres, may, as Dr. Alison justly remarks, 2 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 

 half the time of the whole pulsation, it must be accomplished in ^Jgth of 

 a minute, or 7> 3 ths of a second. Again, it is certain 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: every one of these must require a 

 separate 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 -g-^jj-jth P art ^ a nn 'nute, or in -g^th of a second. Haller cal- 

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

 take place in less than -^-ggth of a second, for many minutes at least in suc- 

 cession. 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 ( 639). From these data, it 

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

 air innny 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 chordce vocules, which are possessed of a very considerable de- 

 gree of elasticity ( 697). According to the observations of Miiller, 3 the 

 average length of these, in the male, in a state of repose, is about T 7 3 oths 

 of an inch; whilst in the state of greatest tension it is about T 9 () 3 ff ths; the 

 difference therefore being T ~ ths, or one-fifth of an inch: in the female 

 glottis, the average dimensions are about jVoths and T 6 ,, 3 ths respect- 

 ively; 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, 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 y^^th of an inch. And 

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

 performances of a practiced vocalist. 4 



1 See the experiments of Dr. Poore, Practitioner, January, 1873. 



2 Cyclopaedia of Anatomy and Physiology, Art. Contractility. 



3 Elements of Physiology, Btily's translation, p. 1018. 



4 It is said that the celebrated Madame Mara was able to sound 100 different in- 



