[ iSi ] 
The mufcular fibres when irritated of- 
cillate, contract towards the middle, be¬ 
coming by this means fhorter, thicker, 
hard and wrinkled, and alternately with¬ 
draw themfelves from the middle with 
fitch a degree of velocity as to elude calcu¬ 
lation. 
The flighted; irritation, whether mecha¬ 
nical or chemical, is fufficient to put the 
irritability into immediate aCtion, which 
does not ceafe till after a feries of alternate 
contractions and relaxations. The fibre 
then becomes as long, fmooth, and lax, 
as it was before it received the impulfe. 
The mufcles of dead fubjeCts, or mufcles 
extracted from the bodies of live animals, 
retain this power a much fhorter time than 
that of the deadforce , 
As the mufcular fibres in their aCtion 
fhorten and become thicker and rougher, 
it is natural for the mufcles themfelves to 
acquire the fame properties. 
n 3 
Different 
