STRIATED MUSCULAR FIBRE. 403 



have been held. This property, however, diminishes in proportion 

 to the duration of the contractions of the fibre, and is not again re- 

 covered till the fibre has had time to rest. It does not appear to 

 depend upon the constant influence of the spinal cord, or on any 

 other merely nervous agency. But that it depends merely on a 

 healthy nutrition, and is the expression of the fitness of the muscle 

 for action, is rendered quite probable from the effect of rest in 

 restoring it, and from the loss of tone and the flabby state which are 

 consequent upon long-continued exertion. This tensive force being 

 constantly exerted in ordinary circumstances, produces the some- 

 what flexed position of the limbs in a sound sleep ; since the flexors 

 are so inserted as to act to greater advantage than the antagonizing 

 extensors, though actually less strong than the latter. It also ac- 

 counts for the habitual closure of most of the sphincter muscles, and 

 the deviation, to one side, of the tongue or of the mouth when the 

 muscles of the opposite side are paralyzed. In all similar cases, 

 the sound muscles are not in a state of incessant contraction, as often 

 asserted ; but merely in a state of tension, and at rest, while the 

 antagonizing muscles have lost both their contractility and their 

 tonicity. 



The use of the muscles is inferred from the preceding remarks, 

 and will be particularly specified in the second section of this 

 chapter. 



Modifications of the Contractility of the Striated Muscular Fibre. 



1. An increased or an irregularly acting contractile force of the 

 striated fibres constitutes spasm. If the^contraction is constant, it 

 is termed tonic spasm (as tetanus, trismus, &c.) ; if irregular and in- 

 termitting, it is clonic spasm, or convulsions (epilepsy, chorea, &c.). 



2. A loss of contractility constitutes paralysis, and in which, if 

 complete, all motion is of course impossible. 



3. The rigor mortis is that tonic spasm of all the muscles which 

 usually comes on several hours after death. 



It is in some rare cases entirely absent as after death by light- 

 ning or by asphyxia. It may also be so slight, and last so short a 

 time, as to escape observation. It affects the muscles in the follow- 

 ing order : those of the neck and lower jaw ; those of the trunk ; 

 and those of the lower and the upper extremities. It departs also 

 in the same order. 



It affects all the muscles with nearly the same intensity; the 



