I!
IE
X P E R I M E N T S THE L YMPHA T I C
From each of thcfe receptacles in thè falmorij a canal runs downwards and
inwards, and opens into the upper end of its correfponding vena cava inferior,
contiguous to and on the fore and outer fide of the internal jugular vein. The
terminations of thefe canals are contrafted, and their internal membranes are
doubled, fo as to ferve die purpofe of valves, in preventing the paiTage of the
blood from the vena cava into the receptacles In the cod kind, the receptacles
are proportionally larger than in the falmon ; and, beiides tranfmitting
the mufcles of the gills and their feveral nerves, contain the upper cornua of
the air-bladder (¿).
C H A P T E R V.
EXPERIMENTS and OBSERVATIONS on the SYSTEM of LYMPHATIC
ABSORBENT VESSELS of FISHES.
I. T ^ R O M the want of valves in the lymphatic fyftem of fiflies, except at its
JL termination in the red veins, we can inject coloured fluids from the
large lymphatics into the fmall; and hence trace the feveral parts of the fyflem
much more eafily and diftindly than in the mammalia or in birds. In the
nantes pinnati, where, except in the reticular fubftances of the flomach, the
lymph is contained in veflels nearly of a cylindrical fliape, and remarkably
tough, we can trace the lymphatics with ftill greater certainty than in the pifces
of Linnaeus: For in the latter, from the wcaknefs of the fides of the receptacles
of the chyle and Jymph. x^gir^eat fize, irregular fliape, and numerous communications
with each other, a nipraro-of them, with extravafation and laceration
of neighbouring red veins, happens frequently ; and as the inje£ted Hquors
get thereby into the red veins, we are apt to mlftake thefc for lymphatic
veins.
I have therefore made my experiments chiefly on the nantes pinnati; and have
found, beyond all doubt, that the diftribution of the lymphatic fyftem is univerfal
in them : particularly, by injecting the principal lymphatic from their
head (¿), I have difcovered numberlefs lymphatics in their brain, eye^ ear,
nofe (i^); in all which places the exiftence of lymphatic veflels has of late been
called in queftion by men of eminence.
2. I would next remind the reader of an obfcrvarion I formerly made, That
the red veins are, in proportion to their arteries, as large in fiflies as in man or
quadrupeds, and yet their blood contains few red particles; and from the vcfl"els
of
Tab. XXVl. /Ig. i. 2. ii. 11. Tab. XXVII, S. Tab. XXVIII. M. N. Tab. XXIX. P. Q^
(/) S«Tab. XXrr. fig. 1.3:. Tab.XXIV. O.P. (/) Tab.XVIIt. RSTUVW. (i)Tab.XXi.
A B S O R B E N T V E S S E L S OF F ISHES.
of their mufcles, and of many other parts, thefe particles are in a great meafure
excluded: from which I concluded, that tlieir colourlefs, as well as their red
arteries, terminate in their red veins.
In a great number of experiments, by injecting penetrating liquors into
the arteries and lymphatic veins of fiflies, I have found it impoflible to make
thefe liquors pafs from the arteries into the lymphatics, or from the lymphatics
into the arteries, except where there was a laceration or rupture of thefe veffels
; yet I have repeatedly injedted their red veins from their arteries.
Hence the lymphatic veins do not feem to be the continuation of the lymphatic
arteries of fiflies; or we are led to fuppofe that, as they do not aflift directly
in circulating the blood, they muft be of ufe by abforbing fluids from the
furface, and from the difi^ercnt cavities of their bodies.
4. From a variety of obfervarions and experiments, we can convince our reafon,
tliat the human valvular lymphatic veins are a fyftem of abforbents; but in
this clafs of animals, I have difcovered that it is poflible to give a deciiive ocular
proof of the truth of that dodtrine, by obferving the effefts of injedting
fluids from the trunks into the fmall branches of the lymphatic veins.
My firft experiments were made upon the la£teal veflels of the flcate and of the
cod. I found that water, and even air which is lefs penetrating, paiTed into the
cavities of the ftomach and inteftines, but with difficulty; and as I could not,
when pufliing my injection, fee the villous coat of thofe parts, I was by no
means certain whether the injection was difcharged from the natural mouths or
beginnings of thofe veflTcls, or from tlie fides of them burft by the force with
which the injcdtion was puflied. I therefore thought of making my experiments
iipon a lymphatic from the external furface of the body; and I judged that the
great lymphatic from the head and fore part of the flcatc (-/) would be the fittcft
for my purpofe, as it is large and its coats nrp rcoi.trJcatily Itrong.
I foon obfcrvcd that my fucccfs exceeded my moft fanguine expectation: For
although i had no doubt that the lymphatic veins began by open mouths, yet I
conceived that thefc muft be fo exceedingly minute, that no clear view could
be got of them, and that the colourlefs part alone of the liquors injected would
exfude. But inftead of this, I found that not only water, but air, milk, quickfilver,
and even oil of turpentine coloured with the powder of vermilion, were
difchargcd upon the furface of the ikin, by a vaft number of diftinil orifices,
placcd at regular diftances from each other: yet the force with which thefe liquors
were injeded was very fmall, and there was no extravafarion into the cellular
fubftance any where under the flcin, or in the iiiterftices of the mufcles^
On the contrary, the preparations of the parts on which thefe experiments were
made, give the moft perfedt and beautiful view imaginable of the vaft number.
and extreme fmallncfa of the branches of thofe vefl"els difpeifed upon the flcin,
mufcles, brain, eye, ear, &c. no where disfigured by extravafation (m). Nay,
I which
(0 5 « T.b, XVIII. fig. I. RSTUW. («) Tab.XXI.