THE SECOND POSITION IS DEMONSTRATED
That this may the more clearly appear to everyone, 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 porosities 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 that place to this place, and
from that point to this one; from the centre to the extremities,
to wit; and from the extreme parts back 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 ingeata, 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 cause 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 medium tightness. A
ligature I designate as tight or perfect when it so constricts 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
ablation 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, die, and finally fall
off.
Ligatures of medium tightness I regard as those which compress a
limb firmly all round, 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 blood-letting,
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 anyone make an experiment upon the arm of a man, either
using such a fillet as is employed in blood-letting, 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 mere 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 medium tightness which is used in bleeding, and it will be
seen that the whole hand and arm will instantly become deeply
coloured and distended, and the veins show themselves tumid and
knotted; after ten or twelve pulses of the artery, the hand will
be perceived excessively distended, injected, gorged with blood,
drawn, as it is said, by this medium 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 ligature. And herein
consists the difference between the tight and the medium
ligature, 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 force of the pulse 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 distended, 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 hidden porosities? Through the veins it cannot come;
still less can it come through invisible channels; it must needs,
then, arrive by the arteries, 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 this is
done suddenly all the veins collapse, and disgorge themselves of
their contents into the superior parts, the hand at the same time
resumes its natural pale colour, the tumefaction and the
stagnating blood having 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
blood-letting: 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
porosities 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 anyone to understand the nature
of the attraction that is exerted by ligatures, and perchance of
fluxes generally; how, for example, when the veins are compressed
by a bandage of medium tightness applied above the elbow, the
blood cannot escape, whilst it still continues to be driven in,
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 a vacuum draw, indeed; but in such
wise only that parts are filled, not preternaturally distended or
gorged, and 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 a vacuum. 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 being 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 velocity.
And now, too, we understand why in phlebotomy we apply our
ligature above the part that is punctured, not below it; did the
flow come from above, not from below, the constriction in this
case would not only be of no service, but would prove a positive
hindrance; 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
ligature 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 other the
channels of influx, the arteries, are impeded.