[ 5^4 1 
cient to comprefs and bring together its fides, . 
If we look into the Heart itfelf, there is nothing- 
more to be found befides its Arteries and Veins, with 
the Blood they contain, the Spirits flowing in by its 
Nerves, and the Tendinous Strings which conneQ: and 
bind its Fibres together. Befides other reafons, the Di- 
latation cannot be afcribed to the firft of thefe, b^- 
caufe the Heart perfifts to dilate and contrad itfeU for 
fome time after it is taken out of the Body. No more 
can it be afcribed to the Influx of the Animal Spirits 
from the Brain, fince according to a calculation made 
on the above-recited Experiment, it is dilated and con- 
trafted above two hundred and forty thoufand times 
in a Dog, after the Nerves which fupply it are cut 
afunder. Monfieur Chirac concludes this work is per- 
formed by the fpringinefs of thefe Tendinons Fibres. 
Thefe by the fides of the Heart receding being over^ 
drained, by their Elaftick power contrad themfelves, 
and confliringe and draw together the Flefliy Fibres ^ 
now thefe being thus lefTened in thicknefs, muft be 
fengthned, and the Heart together with them. He 
thinks the Influx of the Animal SpiritS: may help thefe 
Fibres to preferve their Natural Tenfion, and therefore 
when the Nerves are cut, lofing by degrees their Ela- 
ftick power, the motion of the Heart at laft is fup- 
preft. 
The third and laft Enquiry is, why the motion of 
the Auricles and Ventricles of the Heart is alternate ; 
That is, while the Auricles are contrafted, the Ven- 
tricles are dilated, and fo reciprocally : The continuity 
of the Fibres and their Cells in both Ventricles is a 
good reafon why they ftiould have a contemporary 
motion, and the fame reafon will hold for the Auri- 
cles. But fince in a F^tm the Auricles contrad them- 
felves before the Heart has any fenfible motion, they 
muft neceffarily drive a certain portion of Blood into 
the 
