o8 O B S E R V A T I O N S O N T H E
of the calf direaiy into the other ftomachs. Nay, from the Itrudure of a
gutter which leads from the oefophagus, through the feveral ftomachs, it is
evidently intended that drink Üiould, on particular occafions, pafs from
the oefophagus direaiy into the third or fourth ftomachs, without entering
the firft or fécond ftomachs.
In like manner, in quadrupeds and birds, the inteftina caeca muft be
filled by a regular aflion of the mufcular coat upwards, and emptied by that
motion reverfed.
lo. When the blood irritates the auricle or ventricle of the heart, thefe
contrad with fo fudden a jerk, that the blood is thrown from them nearly
in the fame manner as if a blow had been given to thefe organs by an external
agent. Hence, perhaps, wc cannot, as Dr Hales has fuppofed, determine
the force of the heart by obferving the height to which the blood
afcends in a tube inferted into a large artery, or we lhall only be able to determine
that when we can reduce to calculation the effeft of the vis percuffionis.
The force and frequency of the aélion of the heart are generally proportioned
to the quantity and quality of the blood. But, when a very great
quantity of the blood has been loft by a wound, the pulfe becomes more
inftead of lefs frequent. From which we may obferve, that the action of
the heart is regulated not merely by the quality or quantity of the blood,
nor by the diftenfion of the fides of the heart, but alfo by the ufes which
an increafe of the frequency of its anions may ferve.
' The aftion of the heart is alfo greatly influenced by the paflîons of the
mind.
II. When
N E R V O Ü S Y S T E M . 99
11. When the mufcle of a living animal is laid bare, and punilured, or
Dtherwife irritated, it afts fomewhat in the way the fubcutaneous mufcle
of a horfe does when his ikin is ftung by a fly.
12. Several of the above mentioned aftions are varied in force and frequency
after the mind has been difturbed by its proper paiTions.
13. Over fome of thefe ailions the will pofleffes powei', as over refpiration.
This power is not, however, abfolute, but limited.
E T. II.
AN unprejudiced reader, after reviewing thefe fails, would probably be
much furprifed to learn, that men of genius and knowledge had attempted
to prove, that fuch various and complicated aftions were produced by the
mechanical ftrufture of the bodies of animals; and, particularly, that they
chiefly, or entirely depended on the connedlion which our different nerves
have with each other, by being inclofed in the fame iheaths of the dura and
pia mater, or by being joined in ganglia.
Whilft fuch notions were prevalent in fome part of this, as well as in
other univerfities, I thought it neceffary, in order to deteft the fallacy
more clearly, to treat of the fubjedl at confiderable length, and to ftate and
confider all the principal examples of fympathy mentioned by authors, and
to point out the real caufes of the various aflions. But as, of late years,
fuch theories have been gradually lofmg ground, and are now become almoft
obfolete, I fliall content myfelf with copying verbatim the general
heads of my obje<^ons to the doftrine of fuch fympathy on mechanical
principles, on which I have ledured in 1758, and from that to the prefent
time.
That we arc not, from connexion of nerves, to explain the regular motions
of our different organs produced by gentle and ufual ftimuli, is proved
by the following obfervations.
I. Mufcles