VITAL PROPERTIES OF MUSCLE. 



peculiarities observed in its mode of action, it appears probable that the 

 contraction of this kind of muscle, is effected in all cases simply by a 

 closer approximation of the constituent parts of the primitive fibrils 

 without any change taking place in their general direction, without 

 the production of any zig-zag inflexions. In addition to the several 

 reasons stated by Professor Miiller,* for considering this approximation 

 of particles, as at least one of the modes in which the fibres become 

 shortened, must be mentioned the conclusive observations of Mr. Bow- 

 man^ and Professor Ed. Weber,]; both of whom have examined mus- 

 cular fibre during its state of contraction. Mr. Bowman's observations 

 were chiefly made on the fibre of muscles which were spontaneously 

 passing into the state of rigor mortis. He noticed that at the contracted 

 part of the fibre, the transverse strise were approximated closer to each 

 other than elsewhere, and gave to the fibre at such parts a somewhat 

 darker appearance than was presented by the uncontracted portions. Pro- 

 fessor Ed. Weber's observations were made on muscular fibres while con- 

 tracting under the influence of an electric current from a rotatory magnet. 

 He states that, under such circumstances, the contraction may be observed 

 to be attended by a simple shortening and thickening of the individual 

 fibres; and that in this shortening, every part of the contracting fibre parti- 

 cipates, so that the outline of the fibre remains uniformly straight, and pre- 

 sents no appearance either of zig-zag inflexions or of the beaded or knotted 

 characters described by Mr. Bowman. The zig-zag inflexions, however, 

 are produced immediately on the cessation of the contraction, and result, as 

 shewn also by Mr. Bowman, from the resistance which the fibres meet, 

 in their endeavour to elongate to their former state, during relaxation. 

 In the case of individual fibres beneath the microscope, this resistance is 

 caused by friction on the surface of the glass. In other cases it pro- 

 bably results from the fibre, though itself relaxed, being prevented from 

 elongating, and its ends thus kept approximated, by the contraction of 

 neighbouring fibres, or by its not being stretched by the action of an- 

 tagonist fibres. Any of these circumstances would be sufficient to produce 

 the wavy zig-zag appearance frequently observed: and, it may now be 

 considered as tolerably certain, that such an appearance indicates, as Pro- 

 fessor Owen and Dr. Allen Thomson originally supposed, that the fibre is 

 in a state of relaxation, and it may likewise be assumed that in all cases 

 the contraction of muscle is effected by the closer approximation of its 

 component particles without the fibres themselves being thrown out of the 

 straight line. It should be stated, however, that Valentin continues 

 opposed to this view, and still considers the contraction to be attended by 

 the production of zig-zag flexures. 



* Physiology, p. 889. f Philosophical Transactions, 1840. 



J Archives d'Anat. Gen. et de Phys. Janvier, 1846. 

 $ Lehrbuch der Physiol. des Menschen, b. ii. p. 33. 



