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Observations on the propulsion of lymph through the mesenteric lymphatic vessels of the living rat.

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Department of A n a t o m y , College of Medicine, Unimersity of Illinois, Chicago
A study of the mesenteries of the white rat revealed the
feasibility of making a microscopical examination of the large
lymphatic channels which accompany the mesenteric blood
vessels. Consequently, the present investigation was undertaken in an attempt to study these vessels in life under conditions which were as little altered as possible from the normal.
The body wall of the anesthetized rat was opened along the
linea alba, a distance sufficient to permit the withdrawal of
a segment of the gut with its mesentery. The rat was then
placed on an animal board and the mesentery exposed for
microscopical examination. It was soon observed that in
order to study the lymphatics, the surrounding fat must be
reduced. As a result, most of the animals used in this study
have undergone a period of inanition extending from 5 to
8 days.
Approximately fifteen animals were studied before an attempt was made to obtain permanent records of the changes
which take place in the living lymphatics as they propel their
fluid. Permanent records were made by taking photomicrographs of successive stages of activity. F o r this purpose, a
Leitz ‘Miflmca’ camera and Eastman ‘Superpanchromatic’
film were used. In general, low magnification ( X 24) was
employed, and the time of exposure ranged from 1/125 second
t o 1/25 second, depending on the type of filter.
I n their study of the growth of lymphatics as seen in the
transparent chamber introduced into the rabbit’s ear, Clark
and Clark ( ’32)l describe the movement of lymph in these
vessels “to be a bobbing back and forth, synchronous with
the heart beat or respiration, with only a sluggish, jerky, f o r ward progression. ”
These observations do not conform with the well-known
fact that in all laboratory animals a definite progressive flow
of lymph can be observed in the larger channels-especially
the thoracic duct. In the human, under certain pathological
conditions, this definite, regular flow of lymph is observed.
The movement that Clark and Clark describe may be the
result of the lack of valves within the lymphatic vessels that
grow into the chamber, which, because of their nature as
terminal radicles, possess a sluggish current. Other authors
have confined their study to fixed material, and from observations of the presence of muscle fibers and their innervation,
they have assumed logically that the lymphatics contract.
The first animals t o be studied during the course of this
investigation were healthy, well-nourished rats. Although it
was impossible to take photographs of the vessels because of
the surrounding fat, certain advantages of making a study o f
these were evident. These vessels were protected by the fat
from external environmental conditions introduced by the
exposure of the mesentery. Due to difference in light refraction, their course could be seen. Contractions were observed
at intervals along the line of the vessel which were evidenced
by the movement of the fat cells surrounding the particuIar
lymphatic. I n a rat having a respiration rate of 74 and a
heart rate of 168 per minute, it was found that the rate of
contraction of a lymphatic vessel was 12 per minute. In
portions of such a vessel not deeply embedded in fat, cells
could be seen passing through it at an even rate of speed,
making continual progress toward the more central lymphatics.
‘Clark, E. R. a n d E. L. Clark. 1932. Observations on the new growth of
lymphatic vessels as seen in the transparent chambers introduced into the rabhit ’s
ear. Am. J. Anat., vol. 51.
A continuation of this study on rats which had undergone
a period of inanition revealed more clearly the lymphatics
which were contracting. Their valves were discernible. A
wave of contraction usually originated in the region of the
valve sinus. The entire contraction was divided into two
phases : the first, a slow movement concerned chiefly with the
eradication of the space of the sinus, and a second, more
rapid movement which continued centrally almost obliterating the lumen of the vessel. This was followed by a relaxation of the walls. These contractions were segmental, confined to the portions between valves. Each segment of the
lymphatic seemed to be timed with the neighboring segments
so that the contractions served to propel the fluid within the
vessel as a whole (fig. 1). This is the type of movement
observed within the lymphatics, the segments of which were
contracting at a rate between twelve and eighteen times per
minute. Such a picture was seen in nearly all vessels which
had received a minimum of manipulation and exposure.
It was possible to make a more leisurely study of the movements of these vessels after the mesenteries had been exposed
for a period of time. Although the circulation of blood
remained almost normal, lymphatic circulation became much
slower. The movement was sluggish, quite similar to that
described by Clark and Clark. A noticeable increase in blood
cells occurred within the lymph. Frequently the contracting
segments of the vessels were no longer in time with each
other. As a consequence, the lymph was churned back and
forth making only occasional progress toward the central
vessels, I n such a vessel, it was possible to study the effectiveness of valve flaps. Their action seemed to be purely
passive. I n the event of a reversal in the flow of lymph,
part of the fluid at first streamed back through the opening
between the two valve flaps, while the more peripheral parts
of the current exerted pressure on the walls of the valve
sinuses, tending to distend them (fig. 1C). The pressure
of the fluid within these sinuses soon became great enough to
force the mid-portions of the flaps together, thus obliterating
the channel and preventing further regurgitation through. the
valve (fig. 1 D). Ordinarily, during the circulation of the
lymph the valves along the regular channels act apparently
as an emergency mechanism.
As shown by actual observations, the same cannot be said
of the valves which protect the tributaries at their point of
junction with the larger channels. The larger vessel usually
has a valve located just peripheral to the opening f o r the
smaller. The valve of the smaller vessel is located almost at
its point of entrance into the larger. Under this arrangement both valves are called upon to assert their functional
activity continually.
Realizing the inadequacy of descriptive terms in giving a
complete picture of the activity of living lymphatics, the
writer is now making cinematographic records of these vessels, as a supplement t o this work. Certain aspects of the
investigation are being continued. Sufficient data have not
been collected to determine whether o r not peristalsis of the
gut has any effect on the movement of the lymph in this region. Some evidence has been obtained which indicates that
the rate of the circular contractions is not synchronous with
the movement of the lymphatic walls.
I n conclusion, it can be said that the lymph within the lymphatic vessels of the mesentery of the rat is propelled by
means of contractions of their walls. These contractions are
segmental, occurring in sections of vessels between valves.
Fig. 1 Photomicrographs a d explanatory sketches of a series of changes
occurriiig in the walls of a portioii of a meseiiteric lymphatic during a wave of
contraction. X 60. Contractions in this vessel were slow, taking place at a
rate of three times per minute. As indicated by the position of the valves ( 1 and
Z ) , flow of lymph i n this vessel was normally from right to left. A) entire portion
of vessel partially relaxed. Valves 1 and 2 are open. B) peripheral segment
contracting, forcing lymph through valve 1. Wave of contraction coutinues
through segment, 1-2, propelling lymph through valve 2. C ) reversed current
of lymph has closed valve 2. Segment 1-2, only partially relaxed. Pressure
from the reversed flov of lymph is begiiiniiig to disteiid the sinuses of valve 1.
D ) valve 1 completely closed, preventing further regurgitatioii of lymph. Peripheral segment completely relaxed and distended. E ) entire portion of vessel
distended. Movement of lymph ceases uiitil a new wave of contraction is
The rate at which the movements take place is twelve to
eighteen times per minute, which indicates that it is in no way
related to respiration or to the heart beat. The flow of the
fluid is a rapid progression toward the central vessels. The
action of the valves in preventing regurgitation of lymph is
a passive one, depending entirely upon the force of the reversed stream to approximate the valvular flaps.
After this paper was accepted for pxhlicatioii, the author
found that Florey ('27) had published the results of a similar
iiircstigatioii. (Olnscrvations on the coiitracti1it~-of lacteals.
,J. I'hyiol., vol. 62.) Altliougli Florcy did not illustrate his
paper witli fignrcs, our descriptions of the movements of the
lymphatics are ill agreement.
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vessels, living, observations, mesenteric, rat, propulsion, lymphatic, lymph
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