ÏË2
9
OF THE VITAL AND
the pulfe does not depend, folely, upon the quantity of blood thrown
out by the left ventricle of the heart, but alfo upon the more or lefs
difficult paffage of this fluid through the extreme arteries ; fince9
in proportion as thefe are obflruéled or open, a greater or lefs refin¬
ance will be oppofed to the blood projected by the heart* '
After what has been faid of the flownefs of the motion of the
heart in fleep, it will be eafy to fliew why refpiration ffiould be per¬
formed then at greater intervals.
The caufe exciting the alternate contraction of the infpiratory
mufcles, is an uneafy fenfation in the lungs, occafioned by the blood
puffied into their veflels by the right ventricle of the heart *. If
then lefs blood is fent, in a given time, into the lungs in fleep, than
when we are awake, the neceflity of new fupplies of freffi air will
be leflened, and confequently infpiration will be performed at great¬
er intervals.
Further, as in time of fleep the fenfibility of the lungs, like
that of the heart and inteflines, mult be fomewhat impaired, refpi¬
ration mult alfo, on this account, be performed more flowly; for
the infpiratory mufcles will not be excited into acflion till a greater
degree of irritation than ufual be occafioned by the blood accumu¬
lated in the pulmonary veflels. And to this it is owing, that re¬
fpiration is not only flower but fomewhat deeper in time of fleepy
than in a waking perfon at reftin a horizontal pofition.
In comatous and appopledlic cafes, where all the feelings of the
body are much more impaired than in ordinary fleep, refpiration is
not only much flower and deeper than ufual, but, fometimes, after
expiration is finiffied, a paufe of 15, 20, 30, or more féconds will
intervene before a new infpiration is begun. Much the fame
thing happens to animals who have fwallowed too great a quantity
of opium f.
Now, if it be reafönable to afcribe the flow, deep, and interrupted
breathing, in fuch cafes, to the infenfibility which attends thofe dif-
eafes of the head, and whith opium never fails to produce, when
taken
# See fed. viii. above. f See above pag. 104,