THE CIRCULATION OF THE BLOOD IS FURTHER PROVED FROM CERTAIN
CONSEQUENCES.
There are still certain phenomena, which, taken as consequences of this
truth assumed as proven, are not without their use in exciting belief,
as it were, _a posteriore_; and which, although they may seem to be
involved in much doubt and obscurity, nevertheless readily admit of
having reasons and causes assigned for them. The phenomena alluded to
are those that present themselves in connexion with contagions, poisoned
wounds, the bites of serpents and rabid animals, lues venerea and the
like. We sometimes see the whole system contaminated, though the part
first infected remains sound; the lues venerea has occasionally made its
attack with pains in the shoulders and head, and other symptoms, the
genital organs being all the while unaffected; and then we know that the
wound made by a rabid dog having healed, fever and a train of disastrous
symptoms nevertheless supervene. Whence it appears that the contagion
impressed upon or deposited in a particular part, is by and by carried
by the returning current of blood to the heart, and by that organ is
sent to contaminate the whole body.
In tertian fever, the morbific cause seeking the heart in the first
instance, and hanging about the heart and lungs, renders the patient
short-winded, disposed to sighing, indisposed to exertion; because the
vital principle is oppressed and the blood forced into the lungs and
rendered thick, does not pass through their substance, (as I have myself
seen in opening the bodies of those who had died in the beginning of the
attack,) when the pulse is always frequent, small, and occasionally
irregular; but the heat increasing, the matter becoming attenuated, the
passages forced, and the transit made, the whole body begins to rise in
temperature, and the pulse becomes fuller, stronger--the febrile
paroxysm is fully formed, whilst the preternatural heat kindled in the
heart, is thence diffused by the arteries through the whole body along
with the morbific matter, which is in this way overcome and dissolved by
nature.
When we perceive, further, that medicines applied externally exert their
influence on the body just as if they had been taken internally, the
truth we are contending for is confirmed. Colocynth and aloes [applied
externally] move the belly, cantharides excites the urine, garlic
applied to the soles of the feet assists expectoration, cordials
strengthen, and an infinite number of examples of the same kind might be
cited. It will not, therefore, be found unreasonable perchance, if we
say that the veins, by means of their orifices, absorb some of the
things that are applied externally and carry this inwards with the
blood, not otherwise, it may be, than those of the mesentery imbibe the
chyle from the intestines and carry it mixed with the blood to the
liver. For the blood entering the mesentery by the cœliac artery, and
the superior and inferior mesenteries, proceeds to the intestines, from
which, along with the chyle that has been attracted into the veins, it
returns by their numerous ramifications into the vena portæ of the
liver, and from this into the vena cava, and this in such wise that the
blood in these veins has the same colour and consistency as in other
veins, in opposition to what many believe to be the fact. Nor indeed can
we imagine two contrary motions in any capillary system--the chyle
upwards, the blood downwards. This could scarcely take place, and must
be held as altogether improbable. But is not the thing rather arranged
as it is by the consummate providence of nature? For were the chyle
mingled with the blood, the crude with the concocted, in equal
proportions, the result would not be concoction, transmutation, and
sanguification, but rather, and because they are severally active and
passive, a mixture or combination, or medium compound of the two,
precisely as happens when wine is mixed with water and syrup. But when a
very minute quantity of chyle is mingled with a very large quantity of
circulating blood, a quantity of chyle that bears no kind of proportion
to the mass of blood, the effect is the same, as Aristotle says, as when
a drop of water is added to a cask of wine, or the contrary; the mass
does not then present itself as a mixture, but is still sensibly either
wine or water. So in the mesenteric veins of an animal we do not find
either chyme or chyle and blood, blended together or distinct, but only
blood, the same in colour, consistency, and other sensible properties,
as it appears in the veins generally. Still as there is a certain though
small and inappreciable proportion of chyle or unconcocted matter
mingled with this blood, nature has interposed the liver, in whose
meandering channels it suffers delay and undergoes additional change,
lest arriving prematurely and crude at the heart, it should oppress the
vital principle. Hence in the embryo, there is almost no use for the
liver, but the umbilical vein passes directly through, a foramen or
anastomosis existing from the vena portæ, so that the blood returns from
the intestines of the fœtus, not through the liver, but into the
umbilical vein mentioned, and flows at once into the heart, mingled with
the natural blood which is returning from the placenta; whence also it
is that in the development of the fœtus the liver is one of the organs
that is last formed; I have observed all the members perfectly marked
out in the human fœtus, even the genital organs, whilst there was yet
scarcely any trace of the liver. And indeed at the period when all the
parts, like the heart itself in the beginning, are still white, and save
in the veins there is no appearance of redness, you shall see nothing in
the seat of the liver but a shapeless collection, as it were, of
extravasated blood, which you might take for the effects of a contusion
or ruptured vein.
But in the incubated egg there are, as it were, two umbilical vessels,
one from the albumen passing entire through the liver, and going
straight to the heart; another from the yelk, ending in the vena portæ;
for it appears that the chick, in the first instance, is entirely formed
and nourished by the white; but by the yelk after it has come to
perfection and is excluded from the shell; for this part may still be
found in the abdomen of the chick many days after its exclusion, and is
a substitute for the milk to other animals.
But these matters will be better spoken of in my observations on the
formation of the fœtus, where many propositions, the following among the
number, will be discussed: Wherefore is this part formed or perfected
first, that last?--and of the several members: what part is the cause of
another? And many points having special reference to the heart, such as:
Wherefore does it first acquire consistency, and appear to possess life,
motion, sense, before any other part of the body is perfected, as
Aristotle says in his third book, De partibus Animalium? And so also of
the blood: Wherefore does it precede all the rest? And in what way does
it possess the vital and animal principle? And show a tendency to
motion, and to be impelled hither and thither, the end for which the
heart appears to be made? In the same way, in considering the pulse:
Wherefore one kind of pulse should indicate death, another recovery? And
so of all the other kinds of pulse, what may be the cause and indication
of each. So also in the consideration of crises and natural critical
discharges; of nutrition, and especially the distribution of the
nutriment; and of defluxions of every description. Finally, reflecting
on every part of medicine, physiology, pathology, semeiotics,
therapeutics, when I see how many questions can be answered, how many
doubts resolved, how much obscurity illustrated, by the truth we have
declared, the light we have made to shine, I see a field of such vast
extent in which I might proceed so far, and expatiate so widely, that
this my tractate would not only swell out into a volume, which was
beyond my purpose, but my whole life, perchance, would not suffice for
its completion.
In this place, therefore, and that indeed in a single chapter, I shall
only endeavour to refer the various particulars that present themselves
in the dissection of the heart and arteries to their several uses and
causes; for so I shall meet with many things which receive light from
the truth I have been contending for, and which, in their turn, render
it more obvious. And indeed I would have it confirmed and illustrated by
anatomical arguments above all others.
There is but a single point which indeed would be more correctly placed
among our observations on the use of the spleen, but which it will not
be altogether impertinent to notice in this place incidentally. From the
splenic branch which passes into the pancreas, and from the upper part,
arise the posterior coronary, gastric, and gastroepiploic veins, all of
which are distributed upon the stomach in numerous branches and twigs,
just as the mesenteric vessels are upon the intestines; in like manner,
from the inferior part of the same splenic branch, and along the back of
the colon and rectum proceed the hemorrhoidal veins. The blood returning
by these veins, and bringing the cruder juices along with it, on the one
hand from the stomach, where they are thin, watery, and not yet
perfectly chylified; on the other thick and more earthy, as derived from
the fæces, but all poured into this splenic branch, are duly tempered by
the admixture of contraries; and nature mingling together these two
kinds of juices, difficult of coction by reason of most opposite
defects, and then diluting them with a large quantity of warm blood,
(for we see that the quantity returned from the spleen must be very
large when we contemplate the size of its arteries,) they are brought to
the porta of the liver in a state of higher preparation; the defects of
either extreme are supplied and compensated by this arrangement of the
veins.