TheoH 18 TOR: ¥ of /PNDSOESC :T's. 
tended to, as it is very con{picuous in a living 
animal. The blood itfelf undergoes fome con- 
denfation, when violently comprefled by the 
contraction of the heart, and forcibly expelled 
out of it; but is alfoon the other hand fome- 
what rarified, when the heart is dilated by a 
new intromiflion of blood, fo that this natural 
action of the heart and blood correfponds exactly 
with that artificial one of the heart and air in 
the foregoing experiment. 
It may be objected, that naturally in the live 
animal, the air by no means approaches the heart, 
and therefore cannot be repelled by it. But the 
contrary is plain in the cafe of Tadpoles, in 
which we fee the external fkin fenfibly affected 
_ by the pulfations of the heart, and {well out and 
fink in alternately, as that organ dilates or con- 
tracts itfelf, which is the fame as if the air prefled 
immediately againft the heart itfelf. It cannot 
be denied, but that the fame thing muft happen 
in all animals that have lungs and gills, and a 
moveable breaft; nay, it muft, without doubt, 
take place in fome motions of the mufcles. 
If you cut a Frog’s heart out of the body, and 
place itin the glafs fiphon, in the manner before 
defcribed, without firft blowing it up; you will 
plainly fee the drop of water move in the fame 
way it did before, though not fo much as if the 
experiment were made with an inflated heart. 
In the mean time, the water alfo will fink in 
like manner, when the heart contracts  itfelf. 
Experience teaches us, that the defcent of the 
drop of water in this experiment becomes fome- 
times {fo inconfiderable, that it cannot be per- 
ceived, even by the help of the microfcope, 
which is owing tothis, that the heart then con- 
tinues partly contracted, and is not dilated by 
the auricle, which is now become infufficient to 
produce that effect, as it neither propels any 
blood, or air, with which the heart could be di- 
ftended. Hence, of courfe, the contraétion of 
the heart muft become proportionally weaker, 
' and the motion of the water in proportion lefs 
difcernible, But if you blow into the auricles 
at this time, that this auricle, by contracting it- 
felf, may force a quantity of air into the heart; 
the fuccefs of the experiment will immediately 
become much more confpicuous. 
If, inftead of the heart, we thould chufe to 
make ufe of fome other mufcle, we may pro- 
ceed in the manner reprefented in the eighth 
figure, where the glafs fiphon, Tab. XLIX. Fig. 
VIII. 2, contains within its hollow the mufcle, 4, 
and the nerve hanging from the mufcle is faf- 
tened, without being cut or bruifed to a flender 
twifted filver wire, cc, that rans at the other 
end, an eye made in a piece of brafs wire, fol- 
dered to the embolus or pifton of the fiphon, d. 
Things being thus made ready, a drop of water, 
e, muft be let into the flender tube of the fiphon 
by a very fine funnel, Now, if after this, the 
filver wire be cautioufly drawn with a liefurely 
hand f through the ring or eye of the brafs wire, 
till the nerve is irritated by the compreffion, it 
muft by this means undergo, the mutcle will 
contract itfelf in the fame manner with the in- 
flated heart, whofe alterations, upon a fimilar 
2 
127 
occafion, I have already defcribed, even the 
drop of water will in fome meafure fink, though 
afterwards it never rifes again. But this experi- 
ment is very difficultly fenfible, and requires fo 
many conditions to be exactly performed, that it 
mutt be tedious to make it; for which reafon, I 
have bethought myfelf of another that may be 
more eafily underftood and performed. 
You muft have ready a little glafs fiphon, Tab. 
XLIX. Fig. rx. a, cut through with a diamond 
near the extremity of its flender tube, 4; then 
pafs through the hole thus made, the nerve of 
the mufcle c: but as the air can eafily make 
its way through this hole, while the nerve is ir- 
ritated, till it contracts itfelf, fo as to keep the 
water from finking ; it is abfolutely neceflary to 
ftop that paffage on the cutfide, which may be 
eafily done with a little ifing-glafs and ftarch. 
But I muft own, that in this experiment, the 
finking of the drop is fo inconfiderable, that it 
can fcarce be perceived: for this reafon, the 
heart is fitter for this experiment than any other 
muj{cle, asit continues and keeps up for a confi- 
derably long time, and with fufficient ftrength, 
the motion it has once received. 
There are fufficient reafons why this experi- 
ment fhould fucceed better when tried upon the 
heart, than upon the other mufcles; the princi- _ 
pal feems to be this, that in the other mufcles, 
there is no antagonift to dilate them externally, 
nor any blood, which introduced into the blood- 
veffels, can extend them, and difpand the mufcle 
itfelf from withinfide ; though all thefe condi- 
tions are abfolutely neceffary to affect a perfect 
contraction in any mutcle. 
The experiments which were fome time ago 
publifhed with a view of proving, that a quan- 
uty of blood is requifite to contract the mutcles, 
do in reality no fuch thing. Their principal 
weight lies in the conftri€tion of the aorta, ef- 
fected after D. Steno’s method ; but this is truly 
nothing to the purpofe, and can only impofe, at 
firft fight, even upon thofe who examine mat- 
ters of this kind with the leaft circumfpeétion. 
For, by only confidering with a {mall degree of 
attention, that the vertebrz, many nerves, and 
even the {pinal marrow, which are all fattened 
by the ligament, directed by D. Steno, to be 
ufed on this occafion, undergo thereby a violent 
comprefiion, it muft plainly appear, that no con- 
clufions can be fairly drawn from fuch a trial. 
Much lefs can we infer any thing from the other 
experiment, in which the blood is expelled from 
the mufcles, to make room for water introduced 
into them by a fiphon; fince the moving fibres 
of the mufcle are confiderably injured by this 
rough procedure ; fo that this coarfe experiment 
can only fupport a weak argument with unthink- 
ing people, being calculated merely to confirm 
the experiment of D. Steno juft now defcribed, 
Stronger proofs may be reafonably infifted upon, 
to demonftrate a thing of {uch importance, and 
the ligatures of the arteries of the thigh, parti- 
cularly, in Frogs, muft be allowed to bea great 
deal more to the purpofe, 
We ought, however, greatly to commend 
D. Steno’s circumf{pection, in not taking upon 
him- 
