1809.] 
must be obvious, that the nature of he 
pulse; as percepuble to:the touch, must 
depend almost entirely ou the action ‘of 
the heart, since the state of the arteries: 
can produce very little alteration in its 
qualities. . The greater, or less tension 
of the arterial system, may render the 
artery, when at rest, somewhat ‘harder 
oc softer; and. perhaps : avery delicate 
touch may, in some cases, perceive a 
difference im the degree of dilatation, 
although it is seldom practicable to dis- 
tnguish the artery im its quiescent state, 
from the surrounding parts. But the 
sensation which is perceived, when’ the 
artery 1s compressed, as usual, by the 
finger, is by no means to be: confounded 
with the dilatation of the artery; for in this 
case, an Chstacle is opposed to the mio. 
tion of the blood, against which it strikes, 
with the momentum of x considerable 
column, ag a “stream of water strikes ¢ on. 
the valve of an hydraulic anachine ; and 
in this, manner, the pressure felt by the 
finger becomes: nearly equal, ands it 
to. that which is originally exerted by te 
heart’: each pulsation passing under the 
finger, in the same time as is ; ‘equired for 
‘the contraction of the’ heart. Webern 
therefore an artery appears to throb, or 
to beat more strongly than usual, the 
circumstanee is only to be explained 
from: ity greater dilatation, which allows: 
it to receive & greater portion of the 
action of the heart, in the. same-manner 
as an aneurism, exhibits a very strong 
pulsation, _without, any increase — of 
energy, either. in itself, or in the neigh- 
bouring vessels: but when the pulsations 
of the ‘artery: of a paralytic’ arm. become 
feeble, the change is to be attributed to- 
its permanent contraction, since the en- 
largemeut and contraction of the blood 
BAe of a limb, are known. to attend * 
the increase: or- Aeainiison of its mus- 
cular exertions. The dimination of the 
Strength of an artery may increase the 
apparent magnitude of the pulse, by 
diminishing the. velocity. with which the: 
pulsation is transmitted; for ir hus been 
proved by the doctor, that the magnitade 
of the piilse is in the inverse ratio of che 
length of the artery, distended at once ; 
and this length is proportional to the 
velocity of the transmission; but the, 
force of the pulse striking the: finger, 
would not be affected by ‘such change, 
except that it might ‘be rendered’ some-- 
what: fuller, and ‘Softer, although a con- 
siderable throbbing might be felt in the: 
part, from the: increased’ distension of! 
the.temporary diameter ofthearterz, 
Proceedings of Learned & Soé 
CictleSe qi 
Dr. "Young next proceeds to inves- 
tigate the deviations from the hatura! 
state of the circulation, which may be 
either general or partial: the general 
deviations “may consist, either in @ 
change of the motion of the heart, or of 
the capacity of the capillary arteries. 
Wheit the motion of the heart isaffected, 
the quantity of blood tramsmitted by it 
may either reulam the same as in per- 
feet health, or be diminished or ine 
creased. » If it remam the same, (the 
pulse, if more frequent, must be weaker, 
and if slower, it must be stronger; but 
this latter combination is scarcely ever 
observable’; and in the. former case, the 
heart thast cither nex rer be filled, perhaps 
on account of too great irritability; or 
never be emptied, fieor the weakness of 
its muscular powers, When the qual = 
uty of the blood transmitted by the heart 
is smaller than in health, the arteries 
must be contracted, until their tension 
becomes only adequate to propel the - 
blood through the capillary vessels, with 
a proportionally smaller velocity; and 
the veins must becoine distended, unless 
the muscular caats‘of the arteries cain be 
sutficiently relaxed, to alford a dimi- 
nished tension... In this stare, the pulse 
must be weak and small, and the arteries 
being “partly exhausied, there will pro- 
bubly be a paleness and chillness in the 
extremities ; until the bload, which ‘is 
accamulated m the veins, has suihicient 
power to urge the heart to a preater ac- 
tions and perhaps, from the vigour which 
it may have acquired during the re Mis— 
sion of its’ exe: t1ons, even “to a morbid 
excess of activity. Hence a contrary 
state may arise, in, which the quantity of 
blood transmitted by the heart, is greater 
than in perfect health; the pulse wiil then 
be fall and strong, the arteries beingydis- 
tended, so as to be capable of exerting a 
pressure, sufficient to maintam an in- 
creased velucity, and to overcome the 
consequent increa ise Of resistance; a state 
wiiich perhaps constituies the hie fit of 
fever, and which is probably sometimes 
removed: in consequence of arelaxation of 
the extreme arteries, which suffer thesu- 
perfluous blood to pass more easily into 
the veins, Sucha relaxation, when car- 
ried toa morbid extent, may also be a 
principal cause of another general ‘de-~ 
rangement of the circulation, the motion 
ef the blood: being oul anaee and the 
arteries emptied,so that the pulse may be 
small and’weak, while the veins are over 
charged; and the henrt exhausted by vid= 
lent ‘and fruitless efforts, to restore the. 
equilibrium, 
