812 OP THE STRUCTURE AND FUNCTIONS OF MUSCULAR TISSUE. 



supposition that during the active alternate contraction and elongation of 

 the fibres the circulation through the vessels is more rapid, so that the heat 

 locally produced is carried oft' by the blood. The peculiar sound heard 

 during the contraction of striated muscle may be perceived, as suggested by 

 Dr. Wollaston, 1 by placing the tip of the little finger in the ear, and con- 

 tracting the muscles of the ball of the thumb, or by powerfully exerting the 

 muscles which close the jaw. It resembles the distant rumbling of carriage- 

 wheels, or an exceedingly rapid and faint tremulous vibration, which, when 

 well marked, has an almost metallic tone. From various experiments made 

 upon himself and others, Professor Haughton estimates that the number of 

 vibrations varies from 32 to 36 per second. The sound may be readily con- 

 ceived to depend upon the friction of the elements of the muscle, one upon 

 another, which must thus be perpetually taking place so long as it continues 

 in a state of activity, an explanation that receives support from the observa- 

 tion of Helmholtz, that the pitch of the note may be made to vary by ex- 

 citing contraction in the muscle with an interrupted current, the shocks of 

 which succeed one another with varying rapidity. The amount of shortening 

 which a muscle will undergo, bears a direct relation to the resistance; and 

 by opposing a sufficient resistance, the contractile power of the muscle may 

 be powerfully exerted without any contraction taking place. Under ordi- 

 nary circumstances the striated muscles do not contract much more than 

 one-third of their length, being restrained by the mechanical arrangements 

 of the bones and joints, and by the antagonistic muscles. But if a long 

 muscle of a frog be removed from the body and powerfully stimulated, it 

 will contract to one-fifth of its original length. The unstriped fibres will 

 contract under favorable circumstances to about one-third of their length. 



663. Muscles, whether in the contracted or elongated state, possess a cer- 

 tain amount o*f elasticity. By this term is meant that force by which the 

 particles of any substance, after being approximated to or separated from 

 one another, strive to regain their original position. The elasticity of mus- 

 cular fibre is small, but remarkably perfect ; for although it is extended 

 considerably by a light weight, it recovers itself completely on the removal 

 of the extending force. 2 Like that of India-rubber, it is augmented by heat. ' 

 That it is exceedingly small, even during life, is shown, as Mansvelt has 

 observed, 4 by the fact, that in cases of paralysis of the third nerve the pupil 

 is for some days brought quite into the middle of the space between the eye- 

 lids solely through the elastic contraction of the rectus interims ; a proof that 

 its antagonist, in a state of elongation, exercises no force worth speaking of. 

 On appending a small weight to a vertically-suspended fresh muscle, it at 

 first elongates suddenly and considerably (the primary extension), then much 

 more slowly (the secondary extension). On removing the weight, the same 

 phenomena appear in inverse order ; a considerable primary, and a more 

 gradual and smaller secondary retraction. With small weights the increase 

 in length is proportional to the weight ; with heavier weights a greater pro- 

 portional weight is required to produce the same amount of extension, as is 

 shown in the following experiment made by Weber 5 with the Hyoglossus of 

 a Frog : 



1 Philosoph. Trans., 1811. 



2 Heidenbain, Studien, Berlin, IBM; and Wundt, Miiller's Archiv, 1857. 



3 Schmulowitsch, Centralblatt, 1870, p. tiO'.l. 



4 Set- a lie-view of his work in the Med.-Chir. Rev., for 1864, p. 443, vol. i. 



5 Warner's Handworterbuch, Bd. iii, p. 64. See also Volkmann, PHii^cr's Archiv, 

 Bd vii, 1873, p. 15. Fiok, Pfluger's Archiv, 1871, Bd. iv, p. 301, finds that the elas- 

 ticity of muscle varies with each degree of contraction. 



