SOUND OF MUSCULAR CONTRACTION. 46& 



rounder, more prominent, harder, and apparently tougher. 

 But this hardness of muscle in the state of contraction, is not 

 due to increased firmness or condensation of the muscular 

 tissue, but to the increased tension to which the fibres, as well 

 as their tendons and other tissues, are subjected from the re- 

 sistance ordinarily opposed to their contraction. When no 

 resistance is offered, as when a muscle is cut off from its ten- 

 don, not only is no hardness perceived during contraction, but 

 the muscular tissue is even softer, more extensile, and less 

 elastic than in its ordinary uncontracted state (Ed. Weber). 



Heat is developed in the contraction of muscles. Becquerel 

 and Breschet found, with the thermo-multiplier, about 1 of 

 heat produced by each forcible contraction of a man's biceps ; 

 and when the actions were long continued, the temperature of 

 the muscle increased 2. It is not known whether this devel- 

 opment of heat is due to chemical changes ensuing in the 

 muscle, or to the friction of its fibres vigorously acting : in 

 either case, we may refer to it a part of the heat developed in 

 active exercise (p. 190). And Nasse suspects that to it is due 

 the higher temperature of the blood in the left ventricle ; for 

 he says that this fluid is always warmer in the left ventricle 

 than in the left auricle, and that the blood in the latter is but 

 little warmer than that on the right side of the heart. But 

 these experiments need confirmation. 



Sound is said to be produced when muscles contract forcibly. 

 Dr. Wollaston showed that this sound might be easily heard 

 by placing the tip of the little finger in the ear, and then 

 making some muscles contract, as those of the ball of the 

 thumb, whose sound may be conducted to the ear through the 

 substance of the hand and finger. A low shaking or rum- 

 bling sound is heard, the height and loudness of the note being 

 in direct proportion to the force and quickness of the muscular 

 action, and to the number of fibres that act together, or, as it 

 were, in time. 



The two kinds of fibres, the striped and unstriped, have 

 characteristic differences in the mode in which they act on the 

 application of the same stimulus ; differences which may be 

 ascribed in great part to their respective differences of struc- 

 ture, but to some degree possibly, to their respective modes of 

 connection with the nervous system. When irritation is ap- 

 plied directly to a muscle with striated fibres, or to the motor 

 nerve supplying it, contraction of the part irritated, and of 

 that only, ensues ; and this contraction is instantaneous, and 

 ceases on the instant of withdrawing the irritation. But 

 when any part with unstriped muscular fibres, e. g., the intes- 

 tines or bladder, is irritated, the subsequent contraction ensues 



