590 MOTION. 



a fibre which has been recently contracted, and is not at 

 once stretched again by some antagonist 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, an 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 con- 

 densation of the tissue. This has been proved for entire 

 muscles, by making a mass of muscle, or many fibres to- 

 gether, contract in a vessel full of water, with which a fine, 

 perpendicular, graduated tube communicates. Any dimi- 

 nution of the bulk of the contracting muscle would be 

 attended by a fall of fluid in the tube ; but when the ex- 

 periment is carefully performed, the level of the water in 

 the tube remains the same, whether the muscle be con- 

 tracted or not.* 



In thus shortening, muscles appear to swell up, becom- 

 ing rounder, more prominent, harder, and apparently 

 tougher. But this hardness of muscle in the state of con- 

 traction, 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 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 (Ed. Weber). 



Heat is developed in the contraction of muscles. Bec- 

 querel and Breschet found, with the thermo-multiplier, 



* Edward Weber, however, states that a very slight diminution does 

 take place in the bulk of a contracting muscle ; but it is so slight as to 

 be practically of no moment. 



