THE SECOND POSITION IS DEMONSTRATED.
That this may the more clearly appear to every one, I have here to cite
certain experiments, from which it seems obvious that the blood enters a
limb by the arteries, and returns from it by the veins; that the
arteries are the vessels carrying the blood from the heart, and the
veins the returning channels of the blood to the heart; that in the
limbs and extreme parts of the body the blood passes either immediately
by anastomosis from the arteries into the veins, or mediately by the
pores of the flesh, or in both ways, as has already been said in
speaking of the passage of the blood through the lungs; whence it
appears manifest that in the circuit the blood moves from thence hither,
and from hence thither; from the centre to the extremities, to wit; and
from the extreme parts back again to the centre. Finally, upon grounds
of calculation, with the same elements as before, it will be obvious
that the quantity can neither be accounted for by the ingesta, nor yet
be held necessary to nutrition.
The same thing will also appear in regard to ligatures, and wherefore
they are said to _draw_; though this is neither from the heat, nor the
pain, nor the vacuum they occasion, nor indeed from any other cause yet
thought of; it will also explain the uses and advantages to be derived
from ligatures in medicine, the principle upon which they either
suppress or occasion hemorrhage; how they induce sloughing and more
extensive mortification in extremities; and how they act in the
castration of animals and the removal of warts and fleshy tumours. But
it has come to pass, from no one having duly weighed and understood the
causes and rationale of these various effects, that though almost all,
upon the faith of the old writers, recommend ligatures in the treatment
of disease, yet very few comprehend their proper employment, or derive
any real assistance from them in effecting cures.
Ligatures are either very tight or of middling tightness. A ligature I
designate as tight or perfect when it is drawn so close about an
extremity that no vessel can be felt pulsating beyond it. Such a
ligature we use in amputations to control the flow of blood; and such
also are employed in the castration of animals and the removal of
tumours. In the latter instances, all afflux of nutriment and heat being
prevented by the ligature, we see the testes and large fleshy tumours
dwindle, and die, and finally fall off.
Ligatures of middling tightness I regard as those which compress a limb
firmly all around, but short of pain, and in such a way as still suffers
a certain degree of pulsation to be felt in the artery beyond them. Such
a ligature is in use in bloodletting, an operation in which the fillet
applied above the elbow is not drawn so tight but that the arteries at
the wrist may still be felt beating under the finger.
Now let any one make an experiment upon the arm of a man, either using
such a fillet as is employed in bloodletting, or grasping the limb
lightly with his hand, the best subject for it being one who is lean,
and who has large veins, and the best time after exercise, when the body
is warm, the pulse is full, and the blood carried in larger quantity to
the extremities, for all then is more conspicuous; under such
circumstances let a ligature be thrown about the extremity, and drawn as
tightly as can be borne, it will first be perceived that beyond the
ligature, neither in the wrist nor anywhere else, do the arteries
pulsate, at the same time that immediately above the ligature the artery
begins to rise higher at each diastole, to throb more violently, and to
swell in its vicinity with a kind of tide, as if it strove to break
through and overcome the obstacle to its current; the artery here, in
short, appears as if it were preternaturally full. The hand under such
circumstances retains its natural colour and appearance; in the course
of time it begins to fall somewhat in temperature, indeed, but nothing
is _drawn_ into it.
After the bandage has been kept on for some short time in this way, let
it be slackened a little, brought to that state or term of middling
tightness which is used in bleeding, and it will be seen that the whole
hand and arm will instantly become deeply suffused and distended, and
the veins show themselves tumid and knotted; after ten or fifteen pulses
of the artery, the hand will be perceived excessively distended,
injected, gorged with blood, _drawn_, as it is said, by this middling
ligature, without pain, or heat, or any horror of a vacuum, or any other
cause yet indicated.
If the finger be applied over the artery as it is pulsating by the edge
of the fillet, at the moment of slackening it, the blood will be felt to
glide through, as it were, underneath the finger; and he, too, upon
whose arm the experiment is made, when the ligature is slackened, is
distinctly conscious of a sensation of warmth, and of something, viz., a
stream of blood suddenly making its way along the course of the vessels
and diffusing itself through the hand, which at the same time begins to
feel hot, and becomes distended.
As we had noted, in connexion with the tight ligature, that the artery
above the bandage was distended and pulsated, not below it, so, in the
case of the moderately tight bandage, on the contrary, do we find that
the veins below, never above, the fillet, swell, and become dilated,
whilst the arteries shrink; and such is the degree of distension of the
veins here, that it is only very strong pressure that will force the
blood beyond the fillet, and cause any of the veins in the upper part of
the arm to rise.
From these facts it is easy for every careful observer to learn that the
blood enters an extremity by the arteries; for when they are effectually
compressed nothing is _drawn_ to the member; the hand preserves its
colour; nothing flows into it, neither is it distended; but when the
pressure is diminished, as it is with the bleeding fillet, it is
manifest that the blood is instantly thrown in with force, for then the
hand begins to swell; which is as much as to say, that when the arteries
pulsate the blood is flowing through them, as it is when the moderately
tight ligature is applied; but where they do not pulsate, as, when a
tight ligature is used, they cease from transmitting anything; they are
only distended above the part where the ligature is applied. The veins
again being compressed, nothing can flow through them; the certain
indication of which is, that below the ligature they are much more tumid
than above it, and than they usually appear when there is no bandage
upon the arm.
It therefore plainly appears that the ligature prevents the return of
the blood through the veins to the parts above it, and maintains those
beneath it in a state of permanent distension. But the arteries, in
spite of its pressure, and under the force and impulse of the heart,
send on the blood from the internal parts of the body to the parts
beyond the bandage. And herein consists the difference between the tight
and the medium bandage, that the former not only prevents the passage of
the blood in the veins, but in the arteries also; the latter, however,
whilst it does not prevent the pulsific force from extending beyond it,
and so propelling the blood to the extremities of the body, compresses
the veins, and greatly or altogether impedes the return of the blood
through them.
Seeing, therefore, that the moderately tight ligature renders the veins
turgid, and the whole hand full of blood, I ask, whence is this? Does
the blood accumulate below the ligature coming through the veins, or
through the arteries, or passing by certain secret pores? Through the
veins it cannot come; still less can it come by any system of invisible
pores; it must needs arrive by the arteries, then, in conformity with
all that has been already said. That it cannot flow in by the veins
appears plainly enough from the fact that the blood cannot be forced
towards the heart unless the ligature be removed; when on a sudden all
the veins collapse, and disgorge themselves of their contents into the
superior parts, the hand at the same time resuming its natural pale
colour,--the tumefaction and the stagnating blood have disappeared.
Moreover, he whose arm or wrist has thus been bound for some little time
with the medium bandage, so that it has not only got swollen and livid
but cold, when the fillet is undone is aware of something cold making
its way upwards along with the returning blood, and reaching the elbow
or the axilla. And I have myself been inclined to think that this cold
blood rising upwards to the heart was the cause of the fainting that
often occurs after bloodletting: fainting frequently supervenes even in
robust subjects, and mostly at the moment of undoing the fillet, as the
vulgar say, from the turning of the blood.
Farther, when we see the veins below the ligature instantly swell up and
become gorged, when from extreme tightness it is somewhat relaxed, the
arteries meantime continuing unaffected, this is an obvious indication
that the blood passes from the arteries into the veins, and not from the
veins into the arteries, and that there is either an anastomosis of the
two orders of vessels, or pores in the flesh and solid parts generally
that are permeable to the blood. It is farther an indication that the
veins have frequent communications with one another, because they all
become turgid together, whilst under the medium ligature applied above
the elbow; and if any single small vein be pricked with a lancet, they
all speedily shrink, and disburthening themselves into this they subside
almost simultaneously.
These considerations will enable any one to understand the nature of the
attraction that is exerted by ligatures, and perchance of fluxes
generally; how, for example, the veins when compressed by a bandage of
medium tightness applied above the elbow, the blood cannot escape,
whilst it still continues to be driven in, to wit, by the forcing power
of the heart, by which the parts are of necessity filled, gorged with
blood. And how should it be otherwise? Heat and pain and the _vis vacui_
draw, indeed; but in such wise only that parts are filled, not
preternaturally distended or gorged, not so suddenly and violently
overwhelmed with the charge of blood forced in upon them, that the flesh
is lacerated and the vessels ruptured. Nothing of the kind as an effect
of heat, or pain, or the vacuum force, is either credible or
demonstrable.
Besides, the ligature is competent to occasion the afflux in question
without either pain, or heat, or _vis vacui_. Were pain in any way the
cause, how should it happen that, with the arm bound above the elbow,
the hand and fingers should swell below the bandage, and their veins
become distended? The pressure of the bandage certainly prevents the
blood from getting there by the veins. And then, wherefore is there
neither swelling nor repletion of the veins, nor any sign or symptom of
attraction or afflux, above the ligature? But this is the obvious cause
of the preternatural attraction and swelling below the bandage, and in
the hand and fingers, that the blood is entering abundantly, and with
force, but cannot pass out again.
Now is not this the cause of all tumefaction, as indeed Avicenna has it,
and of all oppressive redundancy in parts, that the access to them is
open, but the egress from them is closed? Whence it comes that they are
gorged and tumefied. And may not the same thing happen in local
inflammations, where, so long as the swelling is on the increase, and
has not reached its extreme term, a full pulse is felt in the part,
especially when the disease is of the more acute kind, and the swelling
usually takes place most rapidly. But these are matters for after
discussion. Or does this, which occurred in my own case, happen from the
same cause. Thrown from a carriage upon one occasion, I struck my
forehead a blow upon the place where a twig of the artery advances from
the temple, and immediately, within the time in which twenty beats could
have been made, I felt a tumour the size of an egg developed, without
either heat or any great pain: the near vicinity of the artery had
caused the blood to be effused into the bruised part with unusual force
and quickness.
And now, too, we understand wherefore in phlebotomy we apply our fillet
above the part that is punctured, not below it; did the flow come from
above, not from below, the bandage in this case would not only be of no
service, but would prove a positive hinderance; it would have to be
applied below the orifice, in order to have the flow more free, did the
blood descend by the veins from superior to inferior parts; but as it is
elsewhere forced through the extreme arteries into the extreme veins,
and the return in these last is opposed by the ligature, so do they fill
and swell, and being thus filled and distended, they are made capable of
projecting their charge with force, and to a distance, when any one of
them is suddenly punctured; but the fillet being slackened, and the
returning channels thus left open, the blood forthwith no longer
escapes, save by drops; and, as all the world knows, if in performing
phlebotomy the bandage be either slackened too much or the limb be bound
too tightly, the blood escapes without force, because in the one case
the returning channels are not adequately obstructed; in the other the
channels of influx, the arteries, are impeded.