To Dr Duncan, Jun. &c. &c. &c.
1.
Previous to certain dissections by Professor Tiedemann and Dr Fohmann, no one had
doubted that the absorbent vessels conveying the chyle from the small intestines,
and generally called lacteals, proceeded, in the seal as in other animals, to the
mesenteric glands, into which they penetrated, and in which they terminated; from
which glance certain other vessels, in structure quite analogous to those just described,
arose, which vessels terminated in one or other of the branches of the thoracic duct,
contributing very materially towards the formation of the duct, and of the receptaculum, or cisterna chyli, placed usually at the commencement of the duct, and just where it passes through
the diaphragm. The first set of vessels, those conveying the chylous fluid from the
intestines to the mesenteric glands, anatomists have agreed to call vasa afferentia ; whilst the second series, or those carrying the chylous fluid (whether the same
or altered) from the glands into the thoracic duct, have generally been called vasa efferentia. The existence of these latter vessels in the seal has been denied by Tiedemann,
who states, that the chyle, poured into the glands by the vasa afferentia, is absorbed by veins only, arising from these glands, and thus conveyed directly
into the blood, without passing along the thoracic duct. It would follow, were this
account of the anatomy of these vessels correct, that the thoracic duct in these animals
was intended for carrying the lymphatic fluid only, and that the chyle passed into
the general circulation by quite another route,-- but, nothing can be imagined more
incorrect than such a statement. In the specimen of the common seal (Phoca Vitul.
Linn., Seehund of the Germans), which is now lying before me, and from which this
description is taken, I find the lacteal vessels proceeding from the small intestines
to be very numerous, distinct, and injected with chyle; * the greater number of them proceed towards a large mesenteric glad, about four inches
in length, placed close to the spine, immediately behind the turn at the duodenum,
and not far from the pancreas; the remainder of the lacteals pass into two smaller
mesenteric glands, situated close to the former, but somewhat lower down. Into these
glands the lacteals penetrate, dividing very generally into several branches before
dipping into the gland. Near to the lower or smaller end of the largest mesenteric
gland, are seen several branches of lacteal vessels (in the present specimen also
loaded with chyle), arising from the gland, and speedily uniting into a larger trunk.
This, in its course upwards towards the larger or diaphragmatic end of the gland,
is speedily joined by many others from every portion of the gland; these united, form
a large trunk, lodged in a fissure which divides the gland as it were into two, longitudinally.
By the time the duct has reached the larger extremity of the gland, it is very considerable
magnitude, exceeding considerably a crow’s quill, and possessing a valvular structure.
After quitting the gland, it crosses over towards the right side, and mainly contributes
to form the receptaculum chyli, constituting indeed one of its largest branches.†
The receptaculum chyli in the seal is very large ; it is situated close to the aortic passage of the diaphragm,
and may be said to be formed chiefly by two large branches. One of these, the lacteal
branch, (the real vas efferens of the mesenteric glands), has been already described ; the other is situated more
towards the right side, proceeding from the loins and the lower extremities. I traced
it readily to the pelvis. Several other branches, but somewhat less in calibre, join
the receptaculum from the side of the stomach and chest. The thoracic duct is large and regular; it
joins the general venous circulation as usual, by entering the veins near the junction
of the jugular and subclavian of the left side. The fluid contained in the thoracic
duct was much thinner and less opaque than the chyle, which filled as well the vasa afferentia as the vasa efferentia.
The dissection was one of the easiest I have ever attempted; nor can I account for
the extraordinary oversight of Professor Tiedemann in any other way than by supposing
his specimens to have been greatly mutilated, and totally unfit for dissection.¹⁵ The parts have been prepared for demonstration, though, from the great facility with
which the true anatomy was made out, I scarcely deem them of that importance which
otherwise would have belonged to them, had they, instead of merely correcting an error,
established any new fact in anatomical and physiological science.¹⁶
19th March, 1824
2.
In a letter which I had the honour to submit to you on the anatomy of the chyliferous
system of vessels in the seal, (Phoca Vitulina, Linn.), I endeavoured to show, that whatever support the modern doctrine of “absorption
by means of veins”¹⁷ might have derived from the supposed discoveries of Professor Tiedemann and others
relative to the distribution of the lacteal system in the seal, such support must,
for the future, be denied these doctrines, for the reason, that a dissection, performed
as you have seen, before numerous competent judges of such matters, and under the
most favourable circumstances, entirely disproved the discoveries of the distinguished
German anatomist, and set the question, as I think was likewise your opinion, at rest
for ever.¹⁸
Permit me briefly to mention to you certain details which ought perhaps to have been
introduced into my former letter, but which the comparative facility of the dissection,
with such as, in the course of my comparative anatomy studies, I have been accustomed
to perform, induced me to withhold.
The seal I examined had been very recently taken in a net by the fishermen in the
immediate neighbourhood, so that it came into my hands in the freshest condition.¹⁹ The lacteal vessels of the animal, as far as the mesenteric glands, that is, the
vessels usually called vasa afferentia, were filled with the chyle, the fluid naturally belonging to them. The great vas efferens, into which poured numerous smaller ones, congregating as it were from every portion
of the gland, was also filled with chyle; it entered, by a very large trunk, the receptaculum chyli, which in the specimen I examined was comparatively large; nor had the chyle in the
least altered its sensible qualities till after it became mixed with the thinner lymph,
brought into the receptaculum, by several other great branches of lymphatic vessels which entered it, coming from
the posterior extremities, loins, back, &c., and which have been already described.
Hitherto it might be said, that the knife had scarcely been used, and in this perfect
and natural state, the dissection was shown to you.²⁰ Previous to putting up the parts in spirits as an anatomical specimen²¹, I filled the lacteals proceeding from the intestine (which, for brevity’s sake,
I shall hereafter call the vasa afferentia) with quicksilver²²; the metal penetrated the largest of the mesenteric glands, and seemed to reappear
in the vas efferens in its way to join the thoracic duct, but this I afterwards found not to be the case.²³ I beg of you to remark here, that there were filled with quicksilver in the seal
about twenty lacteals, and lacteals only, for I injected those vessels alone which contained chyle. I recommend this caution
strongly to the attention of those engaged in such inquiries.²⁴ It has appeared to me, that after a time the lacteals empty themselves of their natural
fluids, and in this state the minute branches of the mesenteric veins bear a considerable
resemblance to them. It was not thought prudent to push these injections too far,
lest the vessels should rupture, and the preparation (which is to be placed in the
Anatomical Museum of the Royal College of Surgeons) be destroyed. Finally, previous
to placing the preparation in spirits, the vas efferens was opened, and, on gently blowing air into it, the thoracic duct was immediately
filled as high as its passage into the veins.
I conclude then, that, if ever quicksilver found its way into the mesenteric veins
of the seal, on being simply injected into the lacteals proceeding from the intestine
to the mesenteric glands, that such an appearance by no means marks the usual route
of the chyle into the general circulation ; for we have shown, 1st, that there exists
at least one large vas efferens, of a calibre amply sufficient to convey the whole of the chyle into the thoracic
duct; 2d , that this vessel, into which are poured innumerable smaller branches from
every part of the mesenteric glands, is, in the healthy and fresh specimen, filled
with a fluid resembling chyle in all respects; 3d that although quicksilver did not,
at least satisfactorily, pass into this vessel by being injected into the vasa afferentia, we have no reason to think that it may not do so in the very next specimen examined.
Moreover, the vas efferens was filled with its own fluid the chyle, which I imagine to be much more satisfactory
than if filled with quicksilver; and finally, as we shall see in the next letter,
how trifling a pressure will stop the progress of quicksilver through any vessel,
no important inference can be drawn from its appearance or non-appearance in the thoracic
duct, unless supported by more direct testimony, drawn from the true anatomy of the
part. I might add, that I have great doubts whether the vasa efferentia in man can be injected by pouring quicksilver into the vasa afferentia. Who would venture to call their existence into question? Yet we have no other proofs
of their presence than what I have offered in the seal, viz. their demonstration by
dissection ; their direct continuity with the thoracic duct ; the origin of their
roots in the mesenteric glands ; lastly, their injection with chyle. *
But there is a class of animals in which the phenomena attending the passage of the
chyle into the mass of blood, differ in several respects from what occurs in man and
in other mammiferous animals ; and it has been suggested to me, that perhaps Professor
Tiedemann’s views might have been directed chiefly to the class of animals I now speak
of, viz. the cetaceous mammalia.
As early as 1795, my much respected preceptor, Mr John Abernethy²⁵, demonstrated, that in the whale (the specimen was a male of the genus balæna) there are two ways by which the chyle can pass from the intestines into the
thoracic duct ; “one of these is through those lacteals which pour the absorbent chyle
into bags (mesenteric glands), in which it receives an addition of animal fluids.
The other passage for the chyle is through those lacteals which form a plexus on the
inside of the bags ; through these vessels it passes with some difficulty, on account
of their communications with each other ; and it is conveyed by them to the thoracic
duct, in the same state that it was when first imbibed from the intestines. ” *
The peculiarities in the anatomy of the lactiferous vessels of the whale, as discovered
and first described by Mr Abernethy, are important. There are vasa afferentia which are continuous with the vasa efferentia, and with the thoracic duct. † But as the lacteals open into the interior of the mesenteric glands (which are in
this animal hollow internally) by sufficiently wide orifices, and pour the chyle into
a central cavity, into which also enter numerous veins and arteries, also by large
and distinct orifices; it must be evident, that when quicksilver is poured in sufficient
quantity into these cavities through the vasa afferentia, it will more readily find its way into the general venous system than into the thoracic
duct, by reason of the smaller size of the respective vessels. But though this happens
to quicksilver in the dead body, every physiologist knows, that a precisely inverse
law may take place in the living ; and it is sufficiently remarkable, that in the
Memoir of Mr Abernethy on the Anatomy of the Whale²⁶, that eminent physiologist, though he found numerous orifices of veins entering into
the central cavities of the mesenteric glands in that class of animals, does not therefore
infer that the chyle passes into these veins ; on the contrary, he infers that there
are vasa efferentia which absorb the chyle so poured out ; but it is matter of regret, that the existence
of such vessels was not proved by him.
I became very anxious to ascertain if such an anatomy of the mesenteric glands and
lacteals as had been discovered by Mr Abernethy, existed also in the common dolphin
or porpuss²⁷ ; for I had been assured by a friend, that he had seen a specimen in which the quicksilver,
injected into the vasa inferentia, passed readily into the mesenteric veins, and so into the general circulation. In
the first specimen I examined, I observed that quicksilver did pass from the mesenteric
glands into the vena portæ, by means of a small vein, though not in any great quantity. But this did not happen
until the animal had lain nearly three days on the dissecting table, in very sultry
weather, and until I had injected rather more than sixty lacteals.
By this time the chyle had disappeared from numerous vessels, and in many instances
they were not easily detected. In the second specimen of this animal, dissected lately
by me, though more than eighty large lacteals proceeding from the intestines, to the
mesenteric gland, were filled with quicksilver, not a globule could be detected, either
in the veins or in any vessel or vas efferens, which could be traced to the thoracic duct. * The reason of this I imagine to be, that the radicles of the vasa efferentia are very small, and that these vessels do not collect into one or two large branches,
in the manner of most other animals, but proceed directly to the next plexus of absorbents,
which in the dolphin supply the place of the receptaculum chyli. With all my efforts, and after the most careful dissection, I could only trace distinctly
two other vasa efferentia, proceeding directly from one of the mesenteric glands, into a branch continuous
with the thoracic ducts. Moreover it is to be observed, that the mesenteric glands
in the porpoise²⁸ are remarkably firm. I cut open several of them, and found the injected quicksilver
uniformly contained in their proper vessels, whose very thin tunics formed a striking
contrast with the surrounding firm substance, of which the gland is chiefly composed.
Without meaning to deny that there are certain grounds for supposing, that in certain
animals, the chyle may follow a different route in its way to the general circulation,
I may, in the mean time affirm, that we cannot infer, from the passage of quicksilver
into the veins of dead animals, after traversing the vasa inferentia and mesenteric glands, that the chyle in living vessels adopts the same route to
reach the general mass of the blood.†
3.
In my last letter to you, I briefly recounted the circumstances which led me to inquire
into the anatomical distribution of the lacteals in cetaceous animals ; and I detailed
the results (somewhat unsatisfactory) of two extremely laborious dissections. In neither
of these had I seen the vasa efferentia chylifera ; and being at the same time aware, that their existence, so far as I know, had been
merely presumed by preceding anatomists, but had not been distinctly demonstrated,
I felt disposed to think that there might be something in the anatomy of these animals,
not very well understood. Some of the arguments for and against the doctrine of absorption
of the chyle by veins I have stated in the letter immediately preceding this.
The result of the inquiry into the lacteals of the porpoise being thus by no means
satisfactory to me, I availed myself of the first opportunity again of resuming it,
and of conducting the dissection, and injection of the lacteals, somewhat differently.
Having therefore obtained a third specimen of the porpoise, * my first care was to inject with quicksilver a considerable number of the lacteals
high on the mesentery, and nearest to the commencement of the thoracic duct; the whole
mass of the intestines was laid over to the left side, and that no impediment might
be offered to the course of the quicksilver, a circumstance I neglected in my former
dissections, I carefully dissected off the portion of the lower cava and aorta, which
lay immediately over the commencing roots of the thoracic duct. At this stage of the
dissection, I observed numerous vessels filled with chyle proceeding from the direction
of the mesenteric glands towards the thoracic duct, and terminating in it ; I felt
convinced that these vessels were the true vasa efferentia, but unwilling to rest a fact of so much importance on the bare inspection of vessels,
at all times deceptive in their appearance, I proceeded to fill about a dozen of the
lacteals (the afferentia) with quicksilver, after traversing the glands, flowed along the vasa efferentia, mixed with the chyle, and passed directly into the thoracic duct. The number of
the vasa efferentia so filled, might be about six, and the quantity of quicksilver conveyed by them into
the thoracic duct was such as to endanger its rupture. I next distended the thoracic
duct with air, and traced it to its entrance into the veins; the valves of this vessel
were as numerous as I have ever seen them, and the tunics of the duct were stronger
than I expected them to be.
I ought further to mention, that the column of quicksilver used was not more than
nine or ten inches in depth ; yet such was the facility with which the metal traversed
the glands, and penetrated to the thoracic duct, that in order to secure the preparation,
and retain the fluid metal in the vasa afferentia, I was obliged to place a tight ligature immediately outside these glands; previous
to doing this, the vessels (the vasa afferentia) had been twice filled with quicksilver, which had as often disappeared. So many
of the efferentia (which are very numerous) had been cut, that I found it impracticable to arrange
the preparation in any other way. Moreover, I have no doubt that similar results may
at all times be commanded by a little care and patience on the part of the dissector,
and by attention to those circumstances which rendered my first dissections unsatisfactory.
We cannot, I presume, now hesitate in affirming, that the anatomy of the seal and
of the porpoise do not furnish any argument against the long established doctrine
of the transmission of the chyle, the nutrient fluid of the body, to the general mass
of blood, by a peculiar system of vessels, consisting of one set of vessels which
convey the chyle to the mesenteric glands; and of another set of a precisely similar
structure, only somewhat larger, conveying the chyle more or less altered from the
glands to the thoracic duct, and thence into the veins; and it seems proved that there
is no other route by which the chyle passes into the blood, or at least that no necessity
arising out of peculiarity in structure has yet been shown in any animal, for its
adopting a different course. The facility with which the metal reached the vasa efferentia, makes it probable that a structure similar to what exists in the whale, as described
by Mr Abernethy, will also be found in the porpoise ; that is, that certain lacteals
pass directly through the glands, maintaining a comparatively large calibre throughout
; but I mention this merely as a conjecture. It will afford me much pleasure, should
the result of this inquiry meet with your approbation.
Edinburgh, May 1824
Authorial Notes
Note 1: The animal was killed only two days ago.⮐
Note 2: On laying open this large and important vas afferens, which was done throughout a considerable extent, it was observed, that the vessels
joining it from the mesenteric glands had their orifices uniformly leading in one
direction, i.e. in the course of the chyle, and towards the receptaculum chyli, in which direction only the fluid pass, by reason of the numerous valvules of the vas efferens and thoracic duct.⮐
Note 3: I do not expect that physiologists shall set aside the usual arguments in favour of
venous absorption ; but the presence of a vas efferens in the seal, and its great size, and, moreover, the facility with which it may be
seen, render the opinion extremely improbable, not to use a stronger expression, that
the chyle enters the mass of blood by any other route than that of the thoracic duct.⮐
Note 4: Phil, Trans.⮐
Note 5: I suppose them continuous with the thoracic duct ; but it is to be remarked that they
were not traced to that vessel by Mr Abernethy. Neither is it stated, in the Memoir
alluded to, whether or not any lacteals were observed to arise from the cavities contained
in the mesenteric glands, and proceed to join the thoracic duct ; there are important
points in the discussion, and merit a farther minute examination. It is to be remembered,
that the specimen examined by Mr A. had been detached from the animal.⮐
Note 6: It is to be remarked here, that only these vessels were filled with quicksilver which evidently contained chyle.⮐
Note 7: Mr Abernethy remarks, in his admirable Memoir so often quoted, that ‘the ready communication
of these bags (the mesenteric glands) with the veins of the whale, induced me to examine
whether I could ascertain any thing similar in other animals. Air impelled into the
lymphatic glands, however, seldom gets into the veins ; sometimes indeed veins are
injected from their glands, but when this has occurred to me, I have observed an absorbent
arising from the gland, and terminating in the adjacent vein.’⮐
Note 8: The animal was about five feet in length, and proved to be a pregnant female.⮐
Editorial Notes
Note 9: F.R.S.E. here indicates Knox’s status as a fellow of the Royal Society of Edinburgh,
which was Scotland’s national academy of science and letters. It was an award granted
to those deemed “eminently distinguished in their discipline” and indicated outstanding
commitment and achievements in one’s field. In 1783 the society received a royal charter,
resulting in its expansion (“Fellows Archive”).⮐
Note 10: Eldest son of the widely known Andrew Duncan, senior; he was a physician, professor,
and fellow of the College of Physicians at Edinburgh University like his father. He
was also married to Mary Knox, who was likely Knox’s eldest daughter, one of his only
two surviving children of seven (Bates 110).⮐
Note 11: The lacteal system essentially refers to what is now understood as the lymphatic system.
The lymphatic system “consists of an extensive network of vessels deputed to the drainage
of extravasated fluids. The contractility of lymphatic vessels and the presence of
valves are essential for the generation and regulation of the lymph transport.” In
simpler terms, the lymphatic system is more or less an essential part of the immune
system. It is in need of much further study, especially with regard to clinical oncology.
Prior to modern definitions, the lymphatic system was called by the name “lacteal”
because of its easily identifiable “milk-like content”, which refers to chyle. The
17th century was considered the golden age of research into the lymphatic system in
the Western world (Natale et al. 417).⮐
Note 12: Here, Knox is referring to a famous German anatomist (received his M.D.) known for
his landmark contributions to a variety of fields: zoology, embryology, morphology,
and many more. He was especially known for his comprehensive work on fetal brain development,
and his inarguable evidence proving that a fetus has a closed circulatory system separate
from the mother’s ("Tiedemann, Friedrich").⮐
Note 13: The person referred to here is likely Vincenz Fohmann, another German anatomist most
known for his masterful injections of mercury into the smallest lymphatic vessels,
preserved to this day in museums of Heidelberg and Liège (Natale et al. 425-6).⮐
Note 14: Knox will go on to specify that the fatal error he has perceived in Tiedemann’s conceptualization
and/or dissection of the lymphatic system is “absorption by means of veins.” My understanding
is that he aims to complicate this perception by way of proving absorption via blood
vessels rather than veins. Tiedemann had long been known for his interest in “the
absorption of nutrients from the alimentary tract” in relation to lymphatic vessels
by 1820, and it would later inform his work on the spleen. (At the time, little was
known about the function and/or importance of the spleen, and its integration into
the lymphatic system in the process of blood formation--so this was a sign of enormous
progress). So in truth it seems that Knox either may be under a misapprehension, or
is pointing out some small adjustment in the processes outlined by Tiedemann. ("Tiedemann,
Friedrich").⮐
Note 15: This is unfortunately not the first case (nor the last) in which Knox would denigrate
the work of his fellow colleagues with immediate and unabating fervor, insisting on
the superiority of his own work by comparison. Biographical evidence confirms this
propensity, in that an American naturalist named John James Audubon visited Edinburgh
in 1826 and was welcomed with unerring consideration and support from Knox. However,
the moment Audubon asked his fellow scientists to evaluate the work he’d done, Knox
(along with his colleagues) became acerbic and harsh, degrading everything he’d accomplished
all of a sudden. Audubon would note his mixed feelings and disappointment about the
encounter in his own writings (Rosner 95-6).⮐
Note 16: This is an ambitious statement, and in all likelihood untrue. William Hunter won the
Copley medal in 1769 for his astounding strides in knowledge of the lymphatic system.
He observed, much like Knox, that “lymphatics and lacteals were two different features
contributing to the formation of the same network of vessels endowed with absorbent
function. He noted that a dye injected into the arteries fills the veins but never
enters the lymphatic vessels, unless the arterial wall is damaged…unlike veins, lymphatics
are not continuous with arteries” (Natale et al. 423). Although their approaches were
different, both understood the movement of lymphatic fluid via capillaries. If there
is any observation of distinction here, it is likely more minute than he makes it
out to be.⮐
Note 17: This will become evident towards the end of this letter-turned-journal article, but
essentially Knox here is speaking to the discovery of blood vessels and how they transmit
human blood throughout the body, rather than veins. The smallest kind of blood vessels
in the human body are known as capillaries, which vitally connect arteries to veins.
In the lymphatic system specifically, “lymphatic capillaries tend to be larger in
diameter than blood capillaries and are interspersed among them to enhance their ability
to collect interstitial fluid efficiently. They are critical in the drainage of extracellular
fluid and allow this fluid to enter the closed capillaries but not exit due to their
unique morphology. Special lymphatic capillaries called lacteals exist in the small
intestine to contribute to the absorption of dietary fats” (Null et al.). While it
is unclear if Knox’s discovery was truly as groundbreaking as he proclaims it to be
(capillaries were discovered long before 1824 in 1661 by Marcello Malpighi (Pearce)),
there was at least basic merit to sharing this observation with the larger scientific
community (Natale et al. 418). More microscopic aspects of medicine were still in
the process of being discovered and described in detail at the time, and this process
is continuing with regard to the lymphatic system even now.⮐
Note 18: There is something to be said here for Knox’s insistence upon proving Tiedemann wrong,
rather than establishing a new discovery and writing in dialogue with other anatomists,
which appears to be more common practice. The rhetoric and focal point of his argument
(toward only his own merit) suggests the kind of myopia that would fuel his denial
of any negligence in the Burke and Hare murder trials. Furthermore, there is the reality
that his work is built on much of existing anatomical expertise, a footnote in a much
larger accomplishment.⮐
Note 19: Burke said in his official confession that “Knox was present on two occasions when
Burke and Hare delivered murdered bodies, and that in one case he had approved of
a corpse’s freshness, but asked no questions” (Richardson 135). While one can understand
the necessity of keeping organic material intact for the sake of an unmarred dissection,
the implications of two men bringing him a “freshly” deceased body with consistent
immediacy should have been an obvious indication that something was amiss based solely
on temporal logistics. Christison aptly observed as much in his recollection of Knox’s
boasts about receiving a dozen or so bodies in such pristine condition, with the incriminating
revelation that “[Knox] had made very light of this suggestion” when Christison remarked
that the corpses likely had never been buried (and then stolen) at all based on their
condition (Richardson 141).⮐
Note 20: Again, he obsesses over the quality of his dissection tools with perhaps more frequency
than would be deemed appropriate or necessary; certainly the tools at hand do have
some bearing on the quality of one’s work, but this is common knowledge and common
practice.⮐
Note 21: Formerly mentioned in my explanatory essay above, this practice of preserving organic
material “in spirits” (usually meant alcohol) was not limited to mere animal specimens.
Mary Paterson’s body was subjected to the same preservation, but with a much more
perverse intent. Here one can see the beginnings of where Knox’s ardor likely extended
too far; what was once for strictly scientific purposes merged into the realm of misogynistic
objectification. While anatomists and doctors may not all engage in this confusion
of priority or intent, it is clear that the working class had ample reason to suspect
the intentions of certain anatomists and doctors. No one person is immune to such
biases or misconduct.⮐
Note 22: Quicksilver is liquid mercury, often used in a variety of scientific endeavors. Naturally
as a result of the toxicity of mercury vaporization at room temperature, this substance
is no longer commonly used in this kind of research, and when it is, the utmost precautions
are taken. The silver substance was used in anatomical experiments in order to reveal
the movement of certain body fluids throughout the body, as the silver coloring and
permeation was easily visible to the naked eye.⮐
Note 23: Part of why liquid mercury was so effective in tracing the lymphatic system in particular
is the fact that “lymphatic vessels…form a largely invisible, delicate and intricate
network…[it seemed] more indefinite, elusive and mysterious” (Natale et al. 418).
While lacteals have a white liquid (chyle) inside that render them more visible in
the body, lymphatic vessels elsewhere “contain[ed] a clear water fluid that render[ed]
them nearby invisible and their presence was very difficult to be documented” (Natale
et al. 423).⮐
Note 24: To Knox’s credit, part of why anatomical investigations into the lymphatic system
were so few was due to the exceptional technical difficulty of such procedures necessitating
liquid mercury injections for a meaningful dissection. British surgeon John Sheldon
explained in 1784 that “the difficulty of dissection is increased, from the necessity
of injecting with quicksilver: for if we happen to wound the vessels, our labor will
be lost by the escape of that subtile fluid” (Natale et al. 423).⮐
Note 25: John Abernethy was a well-known surgeon from this period, born in London and primarily
working at St. Bartholomew’s hospital. He was best known for his skill as an anatomy
instructor; he was so sought after that the hospital eventually had to build a lecture
theater to accommodate the endless stream of his incoming students (Jacyna). Both
Knox and Christison studied under him, which may explain the uncharacteristic deference
with which Knox refers to Abernethy.⮐
Note 26: I was unable to find any larger works (e.g. a book) with this same title. The closest
match I could find was a journal article titled “Some Particulars in the Anatomy of
a Whale” from the Philosophical Transactions of the Royal Society of London in 1796.
Knox’s description also aligns with the contents of this article, suggesting the veracity
of this identification (Home and Abernethy 27-9).⮐
Note 27: Now obsolete form of the word porpoise; not a typo.⮐
Note 28: It is not entirely clear why Knox uses two different forms of this word, there does
not appear to be a greater purpose.⮐