Bauhaus-Universität Weimar

i. Stimuli applied to the mufcles of animals, when laid bare, in« 
(lead of only one contraction lading for a condderabie time, pro¬ 
duce feveral contractions and relaxations alternately fucceeding each 
other, which become gradually weaker, and are repeated after longer 
intervals, as the force of the irritating caufe is diminifhed*. Now, 
thefe alternate contractions are eafily accounted for, if we fuppofe 
them to proceed from a fendent pkinciple, which, in order to the 
getting rid of the pain or uneafy fenfation that arifes from the irri¬ 
tation of the mufcle, determines the influence of the nerves into its 
fibres more ftrongly than ufual. For, if by one or two contractions 
the irritating caufe be thrown off, and, with it, the difagreeable 
fenfation removed, the mufcle will return to its former date of red ; 
Æ otherwife, it will continue for a longer time to be agitated by al¬ 
ternate convulfive motions, which will be more or lefs forcible, and 
repeated after fhorter or longer intervals, in proportion as the fiimu- 
lus and painful fenfation hence enfuing are dronger or weaker. The 
titillation of a dighter ftimulus will be fo much weakened by the drd 
contraCiion of the mufcle, that fome fpace of time mud intervene 
before it will be able to produce a fécond : whereas the fmart pain 
which follows a drong irritation, affeCts the fendent principle fo 
powerfully, that no fooner is the mufcle relaxed, than a new contrac¬ 
tion fucceeds. Thus a gentle irritadon of the left orifice of the do¬ 
rn a cli occadons only a dighter hiccup or convuldve contraction of 
the diaphragm, which, too, is not repeated till after condderabie 
paufes ; while a greater irritation, not only excites dronger convul- 
iions of this mufcle, but alfo a quicker repetition of them. 
'Why the fendent principle, in confequence of a painful fenfation, 
does not keep dich mufcles as are irritated in a continued date of 
contraction, but differs them to be alternately relaxed, fhall be after¬ 
wards explained. 
If the contraction of an irritated mufcle were owing to the aCtion 
of theßimulus upon it as a mere mechanical organ, then, fo long as 
the fiimulus continued to aCt equably, the mufcle ought to remain 
equally contracted, and, upon its ceadng, the mufcle ought to be re- 
R laxedy 
? Seft. i. No, io, and u. above.


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