MUSCLE-NEBVE PHYSIOLOGY. 515 



sound heard was the first overtone. But this rate has been called into 

 question by later experiments, in which a tambour, connected with a 

 recording apparatus, is placed on a contracting muscle. The rate of 

 vibration thus obtained is stated to be from 8-12 per second, according 

 to the muscle investigated and its condition. Tremors are shown by a 

 muscle in fatigue and in many conditions of disease. Since the reso- 

 nance tone of the membrana tympani corresponds to 36-40 vibrations a 

 second, the muscle sound does not indicate the numbei* of vibrations in 

 a contracting muscle. 



(3.) Changes in Shape. There is a considerable difference of opinion 

 as to the mode, in which the transversely striated muscular fibres con- 

 tract, The most probable account is, that the contraction is effected 

 by an approximation of the constituent parts of the fibrils, which, at 

 the instant of contraction, without any alteration in their general direc- 

 tion, become closer, flatter, and wider; a condition which is rendered 

 evident by the approximation of the transverse stria3 seen on the surface 

 of the fasciculus, and by its increased breadth and thickness. The 

 appearance of the zigzag lines into which it was supposed the fibres are 

 thrown in contraction, is due to the relaxation of a fibre which has been 

 recently contracted, and is not at once stretched again by some antago- 

 nist fibre, or whose extremities are kept close together by the contractions 

 of other fibres. The contraction is therefore a simple and, according to 

 Ed. Weber, a uniform, simultaneous, and steady (shortening of each fibre 

 and its contents. What each fibril or fibre loses in length, it gains in 

 thickness : the contraction is a change of form not of size ; it is, there- 

 fore, not attended with any diminution in bulk, from condensation of 

 the tissue. This has been proved for entire muscles, by making a mass 

 of muscles, or many fibres together, contract in a vessel full of water, 

 with which a fine, perpendicular, graduated tube communicates. Any 

 diminution of the bulk of the contracting muscle would be attended by 

 a fall of fluid in the tube; but when the experiment is carefully per- 

 formed, the level of the water in the tube remains the same, whether 

 the muscle be contracted or not. 



In thus shortening, muscles appear to swell up, becoming rounder, more 

 prominent, harder, and apparently tougher. But this hardness of muscle 

 in the state of contraction is not due to increased firmness or condensa- 

 tion 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 

 resistance ordinarily opposed to their contraction. When no resistance 

 is offered, as when a muscle is cut off from its tendon, 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. During contraction in each fibre it is said that the anisotropous 



