[ 3 1 1 ] 
familiar to them, produces thofe frequent fh udders, 
or general mufcular contractions in the whole frame 
of the foetus, which for a fortnight or more are the 
conftant figns, that it has now obtained an animal 
life. 
And here arifes an apparent difference, though it 
will be found the greatefl uniformity, between the 
mufcles of voluntary and thofe of involuntary motion ; 
and namely the heart ; which being appointed to pro- 
trude the vital fluids during the life of -an animal, has a 
fhort alternate remiffion of its contracting caufej and 
is thereby render’d capable of admitting a conftant 
and neceffary fupply of labour and ftimulus together, 
without any force, or contradiction, to the natural 
order of the whole. 
It follows undeniably from what has been faid, 
that if we can prove, that a given mufcle of volun- 
tary motion, does really feel an increafe of the fa- 
miliar warmth of its contained blood, or an equiva- 
lent, to rife and fall inftantly at the command of 
the will, we fhall then duly account for the fub- 
fequent motion. Or, more particularly, if we can 
prove, that the will has a direCt power of heighten- 
ing, increafing, and rendering more acute, the fenfe 
of any nerve, diftributed to a given mufcle, the fame 
familiar politive degree of warmth in the contained 
blood will, to this more acute fenfe, appear to be 
proportionably heightened and increafed, and the 
mufcle (by lemma 2) will inftantly contraCl, and 
continue in that flate during the aCtion of the will 5 
allowing for a fmall feeblenefs, that will gradually 
arife from the gradual exclufion of the contracting 
caufe, and from the blunting of this more acute, and, 
as it were, new fenfation ; which yet, as we fee, may 
