In A Treatise on the Heart Richard Lower attempts to posit
explanations for the movement and color of the blood in the body and for the
mechanisms for which chyle passes into the blood from the ingestion of food, as
well as defining the transfusion of blood and its potential uses. His goal is to further explain the makeup and
difference between the venous and arterial blood, specifically how, and with
what functions, they acquire their differing colors, how transfusion of blood
can be most easily and efficiently obtained between two, living beings, and
what path the chyle makes from the stomach to the blood.
His
first account is on the movement of the blood throughout the body. He believes that the movement through the
septum which was postulated by those who came before Harvey to have been proven
entirely false. Further, the amount of
blood that many of his contemporaries say which escapes from the heart with
each beat is too little and they surely have misunderstood the Harveyan system
(Lower G). He observed that the heart
would always completely fill with blood on diastole and completely evacuate on
systole, that the heart could hold two or more ounces of blood at a time, as
was also observed by Harvey, and that the heart beats at least two thousand
times in an hour. Therefore the amount
of blood ejected by this heart in an hour is over three hundred pounds and
considering that there is at most twenty-five pounds of blood in a man’s body,
the blood must fully circulate the body six or more times within an hour (G 1.2). In order to prove this idea more concretely
he proceeded to sever the cervical arteries of a dog, while holding the aorta
so that no blood could pass through it; after only three minutes the entirety
of the blood within the dog had vacated its body (G 2.2-3). Therefore, because of the quick circulation
of the blood throughout the whole of the body, there cannot be a great
difference between the arterial and the venous blood. What difference does exist, in color, is not
derived from the heating of the blood that takes place within the heart (G
3.2). He undertook another experiment
with a recently deceased dog, in which he removed blood from the dog. The blood which was seen had the bright-red
color as if it had been removed from the artery of a living animal; therefore,
heat alone cannot be the cause of the color of blood (G4). “This red colour is entirely due to the
penetration of particles of air into the blood [in the lungs]” (G4.2).
After
many experiments of injecting beer and wine, among others, into the blood of
animals, Lower had decided to attempt the exchange of blood between
animals. He took three dogs, one of
medium size and two of large size. The
medium dog, which would be the recipient of the new blood, had its jugular vein opened and the blood within it
siphoned off. To replace the lost blood
he introduced the blood from one of the larger dogs until the recipient
appeared overfilled and the process
of draining and replacing was repeated until the two larger dogs had perished
from loss of blood. Upon the stitching
of its wounds the receiving dog awoke and began to jump around as if nothing
was the matter; if anything, he appeared to be more jovial than before, perhaps
because of the new blood within him
(G6-6.2). “There is no reason to think
that the blood of other animals mixes less well with human blood than with
animal blood.” Lower apparently
supervised the injection of sheep’s blood into the body of an insane man on
multiple occasions and saw no perilous results.
Those who have impure blood due to disease or sickness would see no
result other than the continued tainting of the new blood. However, those who would benefit from such
transfusions are people whose bodies have seen tragic losses in blood, as well
as those suffering from arthritis and lunatics (H2).
Chyle
is the substance which is derived from ingested foods and is used in the
replenishment of the blood in the body. In
using ink injected with a syringe Lower proves, to the disdain of many of his
contemporaries, that there is nothing which can be “carried through the
arteries from the spleen to the stomach or vice versa” (H 3.2). The spleen gives nothing directly to the
stomach. There are a great number of
small lacteal vessels throughout the intestines, which allow for the absorption
of the milky cream, chyle, from food
out of the stomach and nothing else. To
confirm this he tied off the intestine of an animal which had recently eaten
and filled them with air. Upon squeezing
the intestines with his hands nothing at all escaped into the lacteal veins. He then repeated the experiment, but with
tinted liquid in the place of air and the same resulted. Therefore, “the lacteal veins do not open
straight and directly into the intestines, but are carried obliquely between
their coats before penetrating into the cavities of the intestines, perhaps in
the same way that the common duct ends in the duodenum, or the ureters in the
bladder.” The absorption of the chyle by
the lacteal veins must take place only when the intestines are at rest and not contracting;
when the veins are open (H 4.2-5). There
appear to be glands, much like those in the mouth, to aid in the dilution of
the chyle for easier absorption and movement throughout the veins (H 5.2). Many more glands exist throughout the ducts,
in order to prevent clotting, en route to the thoracic vessels, and finally the
chyliferous ducts into the subclavian vein.
At the subclavian vein exists a valve which prevents the inflow of blood
into the source of the chyle. (H 5.2-6.2)
Lower conducted two experiments on the subject of the chyle in order to
prove that it only reaches the blood through the chyliferous ducts. He found that if “the passage of chyle
through the thoracic vessels is impeded, the animal, no matter how sated it is
with food, will die within a few days of utter starvation” (H 6.2). The chyle is always flowing into the blood,
but, especially after a large meal, can be distinguished from the blood proper
before it has had time to thoroughly mix.
The substance which exists in the mammary glands, and as milk, is pure
chyle (H 8.2). “The cause of our life
consists in this alone, that the blood in its continuous passage through the
whole of the body carries round heat and nutriment to all the organs, and that
ever-fresh chyle passes into the blood in due measure and amount, restoring
with equivalent supplies the daily loss of blood-fluid and refreshing it with
its continuous inflow” (I 1.2).
Lower
manages to disprove the theory that the heat of the heart is the source of the
bright-red coloration of the blood, and lack of heat the blue-hued
coloration. In doing so he manages to
stumble on the idea of the coloration as an effect of the impact air (not yet
oxygen) has in the blood surfaces it encounters; the lungs aid in this endeavor
by allowing for a greater amount, surface area, of blood to be affected by the
air. Further, he finds that the blood of
animals is not that much different from the blood of humans, and could be used
in transfusion procedures for those who may need additional or altogether
different blood. On the subject of the
chyle, he finds that, most importantly, the liver, and spleen, serve no
function for the life food of the
blood or body, to the discord of the Galenists.
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