350 THE SOLIDS. 



greatly, and is very evident, the strise in the contracted fibre 

 being often one third or even one half closer together than 

 they are in the fibre in its ordinary state of tension. The 

 approximation of the striae to the extent just mentioned, pre- 

 suming the entire length of the fibres to be in a contracted 

 condition, would reduce the length of the muscle in the same 

 proportion, viz. to the extent of a third or even one half. 



Muscular contraction, then, I would define to be a simple 

 shortening of the fibres of a muscle, accompanied by an in- 

 crease in their breadth ; this shortening in the striped mus- 

 cular fibre being evinced by an approximation of the trans- 

 verse striae as well as by an increase in its diameter, while in 

 the unstriped fibre it is manifested solely by an increase in the 

 thickness of the fibrillee. (Plate XL1I. fig. 3. , b.) 



Whether, in muscular contraction, the whole length of the 

 fibres of a muscle is engaged, or part only of their length, 

 or whether, during the continuance of the contraction of a 

 muscle, its fibres remain in a state of quiescence ; or whether 

 they undergo an alternate contraction and relaxation in 

 obedience to the interrupted stimulus derived through the 

 medium of the nerves, it is not easy to determine with cer- 

 tainty ; nevertheless, it is most probable that where the con- 

 traction is very intense and long sustained; such an alternation 

 of condition does exist. 



The stiffening of the body, which occurs after death, known 

 by the terms " rigor mortis," " cadaveric rigidity," is due to 

 muscular contraction. This rigidity usually comes on a few 

 hours after death ; and after continuing for a variable time, 

 not exceeding six or seven days, again disappears. There is 

 much variety, however, in the exact periods of the advent 

 and departure of the rigidity : it has been observed to come on 

 latest, attain its greatest intensity, and to last longest in the 

 bodies of robust persons, who have either died of short and 

 acute diseases, or who have suffered a violent death. On the 

 contrary, it has been remarked to set in soonest and to dis- 

 appear earliest in persons of feeble constitution, and those who 

 have died of a lingering and exhausting malady. 



