1 62 ] 
Mafic. Thus t The Mind intends moving a finger 
to perform a fwift Shake * the firft Motion is a Preft 
fare of the Finger upon the String, by the Con- 
traction of the Flexor of that Finger : The fucceftive 
Motion then will be only a Remiflion of that Pref- 
jurc, without any Nece-flity for a Re*aCtion in the 
antagonift Mufcle, becaufe the Motion required is 
but i n con fider able : And this Preflure and Remiflion, 
by being nimbly repeated, will become a kind of 
alternate Tremor of the Finger upon the Stringy be- 
caufe, after the firft Inflation of the mufcular Cells* 
which caufes the Contraction of the Finger, the -in- 
flam Remiflion of the Inflation becomes a kind of 
Retraction of it, as I have faid before : Them the in- 
terftitial Air follows it with an elaftic ExpanfiOn be- 
yond its Tone of Reft, and comprefies the Cells ; then 
a new Inflation of the Cells fucceeds ; and, in fine, 
an ACtion and Re-aCtion between the interftitial Air 
and Cells is carried on as long as the Shake is re- 
quired to continue : This amounts to an alternate 
Syfiole and TOiaftole between them, like two Springs 
acting by alternate Repulfion. 
XXXI. 
Of involuntary Motion. 
The Performance of the common Actions of Life 
depending upon the voluntary Motion of the Mufcles 
alone, Authors have almoft negle&ed to give any 
Explanation of involuntary Motion; and therefore 
have chiefly attended to the former : Whereas the 
latter as well deferves the Attention of the Learned, 
3 and 
