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(Fig. 43), lasting only fifteen to forty minutes, whereas the increased lymph
flow lasts from forty
minutes to two
hours after the in-
jection. Moreover,
this rise of pressure
in the portal vein
would have more
influence in in-
creasing the capil-
lary pressure in the
intestines than in
the liver. Taking
these facts into con-
sideration, we must
conclude that the
increased lymph flow observed after injection of lymphagogues of the
first class cannot be accounted for by a rise of capillary pressure. It
is open to us to conclude that these bodies act in Heidenhain's sense
on the endothelial cells of the capillaries, exciting them to an active
secretion. It must be remembered, however, that all these bodies are
active poisons. We should expect them, therefore, to diminish rather
than to excite the physiological activity of the endothehal cells. We
have already seen that the effect of a slight injury to or diminished
nutrition of the capillary wall is to increase its permeability. I would
explain the action of these bodies, therefore, as dependent on injury to
the capillary wall, and a consequent enhanced permeability, so that a
pressure which is very Httle above the normal capillary pressure is able
to cause a greatly increased transudation of fluid.

I have already mentioned that these bodies chiefly affect the capil-




Inj. of mussel extract

Fig. 43. — To show effects of the injection of a lyniphagogue of
the first class on the blood pressures in tlie abdominal
organs, and also on the lymph flow. (For explanation of
curves see Fig. 41.)



298 PROD UCTION AND ABSORPTION OF L YMPH.

laries of the liver. Their action, however, is not absolutely confined to
that organ. I have experimental evidence that there is a certain
degree of increased permeabihty of the intestinal capillaries after the
injection of these lymphagogues, an increased permeability which is
brought into evidence only after raising to a certain extent the pressure
in these capillaries. The first class of lymphagogues also affects the
capillaries of the skin. In a number of the experiments in which these
bodies have been injected, we may observe a rapid development of an
urticarial eruption on the skin, and it is a matter of common knowledge
that the ingestion of the animals from which these bodies are derived
(mussels, crayfish, lobster) is often followed in man by an eruption
of urticaria which may or may not be accompanied by other symptoms
of poisoning.

Another substance which seems to act directly on the capillary wall
is curari. This body, however, differs from the class of lymphagogues
under discussion, in the fact that its chief action is on the vessels of the
limbs. The effect of curari in increasing the lymph production in the
limbs was noticed long ago by Paschutin working in Lud wig's labora-
tory. Its direct action on the endothelial wall of the capillaries can be
easily demonstrated in the living frog's web. It may be seen that, after
the injection of curari, the capillary walls become apparently more
sticky, so that the capillaries become filled with a number of leucocytes
adhering to their walls.

Conclusions. — Thus a renewed investigation of the facts discovered
by Heidenhain has shown that they are not irreconcilable with the
filtration hypothesis, but rather serve to support it. At the same
time they prove the extreme importance of the factor upon which
so much stress was laid by Cohnheim, namely, the nature of the
filtering membrane. In fact, we may say that the formation of lymph
and its composition apart from the changes brought about by diffusion
and osmosis between it and the tissues it bathes, depend entirely on
two factors —

1. The permeability of the vessel wall.

2. The intracapillary blood pressure.

So far as our experimental data go, we have no sufficient evi-
dence to conclude that the endothelial cells of the capillary walls
take any active part in the formation of lymph. It seems rather
that the vital activities of these cells are devoted entirely to maintain-
ing their integrity as a filtering membrane, differing in permeability
according to the region of the body in which they may be situated.
Any injury, whether from within or without, leads to a failure of
this their one function, and therefore to an increased permeability,
with the production of an increased flow of a more concentrated
lymph.

We have no evidence that the nervous system has any influence on
the production of lymph in any part, except an indirect one by altering
the capillary pressures in the part through the intermediation of vaso-
constrictor or dilator fibres. This action is better marked in situations
where the capillaries are normally very permeable or where the per-
meability has been increased by local injury to the vessels, or Ijy the
circulation of poisons in the blood stream. ^

^ Cf. Cohnheim u. Lassar, Virchow's Arcliiv, 1878, Bd. Ixxii. S. 132 ; and Jankow-
ski, ibid., Bd. xciii. S. 259.



FORCES CONCERNED IN MO VEMENT OF L YMPH. 299

The Ppiysical Forces concerned in the Movement of Lymph.

We may now consider briefly the forces which bring about the flow
of the lymph and chyle from the origin of the lymphatics towards the
termination of the thoracic duct in the subclavian vein.

In the living animal the lymphatics, like the blood vessels, are in a
condition of moderate distension. The lateral pressure in the lymphatic
duct of the neck was measured in 1849 by Ludwig and Noll.^ In the
dog they found that this pressure varied from 8 to 18 mm. sodium car-
bonate solution. A little later, Weiss ^ measured the pressure in the
same vessel in the dog and horse. In the dog he found that it varied
from 5 to 20 mm., and in the horse from 10 to 20 mm. soda solution.
The latter observer also estimated the velocity of the lymph flow in the
cervical lymphatic by means of Volkmann's hsemodromometer. He
found that the average velocity was about 4 mm. in the second, a
velocity which is exceedingly small as compared with the velocity of
blood in arteries or veins of the same calibre, and is only a few times
greater than the velocity in the capillaries. Since there is a constant
flow of lymph from the periphery to the thoracic duct, it is evident that,
as we trace the lymphatics towards their radicles, the pressure of the
lymph must increase. This increased pressure in the peripheral parts
of the lymphatic system is shown by the fact, to which Paidbeck ^ first
called attention, that if a lymphatic be emptied by pressure, it always
fills from the periphery, and if a ligature be placed round it, the vessel
swells upon the peripheral, and shrinks on the central side of the
ligature.

We see then that the first and chief factor in the onward flow
of lymph is the pressure under which this is formed in the radicles
of the lymphatics and in the tissue spaces. As the blood flows through
the capillaries at a given pressure, a certain proportion of its fluid con-
stituents filteis through the vessel wall, forming a transudation which
is still under a certain amount of pressure, and it is this remaining
pressure which causes the onward flow of the lymph. Hence the
ultimate cause of the lymph flow must be looked for in the energy of
the heart's contraction.

When this hypothesis was first put forward by Ludwig and Noll (in
opposition to the suction theories mentioned previously), it was objected
to by Donders ^ on anatomical grounds. At that time it was thought
that the lymphatics formed a closed system of capillaries, ramifying in
the tissues ; and Donders pointed out that if the pressure in the tissue
juices were higher than that of the contents of the lymphatic capillaries,
the effect would be, not a flow from spaces into capillaries, but a collapse
of the latter with obliteration of their lumen. Further anatomical
investigations have shown us, however, that, in the first place, the
lymphatics are probably not a closed system of tubes, but are in com-
munication with the tissue spaces (Eecklinghausen,^ Ludwig); and
secondly, that the walls of the lymphatics, at any rate in certain situa-
tions, are so connected by strands of elastic fibres with the surrounding

^ Loc. cit.

^ " Experimentelle Untersuch. ueber die Lymphstrom," Dis.s., Dorpat, 1860 (quoted by
Gruenhagen, Bd. i. S. 282).

^ Loc. cit. ^ Ztsclir.f. rat. Med., 1853, N. F., Bd. iv. S. 238.

^ Strieker's "Histology," Syd. Soc. Trans., 1869, vol. i. p. 297.



300 PR OD UCTION AND ABSORPTION OF L YMPH.

connective tissue, that a rise of tension in the meshes of the latter will
only drag the walls of the lymphatics further apart, and thus increase
rather than diminish their lumen. ^

Although the blood pressure is therefore the primary mechanical
factor in the movement of lymph, there are several other factors which,
though subsidiary, are of considerable importance. In the first place, the
flow of lymph through the thoracic duct is much aided by the respira-
tory movements. In all experiments on the subject of lymph formation,
it is necessary to maintain the animal in as quiet a condition as possible,
since any disturbance of the respiratory movements causes a variation
in the lymph flow from the thoracic duct. With every inspiration, in
consequence of the descent of the diaphragm, there is a rise of pressure
in the abdominal cavity, and a fall of pressure in the thorax. Hence
we get an emptying of the lymphatics of the abdomen, including the
receptaculum chyli, and a distension of the duct in the thoracic
cavity. With each expiration the thoracic duct tends to collapse
to a certain degree and so empties itself into the veins, a backward
flow of lymph being prevented by the valves in the duct. If a
manometer be connected by a T-tube with the thoracic duct, it is
found that there is a rise of pressure during expiration and a fall
during inspiration, so that during the latter period the pressure may
become negative.

Eespiration has also an indirect influence on the lymph flow. With
each inspiration the negative pressure in the thorax is increased, so that
a negative pressure is also produced in the intrathoracic venous trunks,
which must cause a suction of lymph through the thoracic duct into the
subclavian vein. That the blood pressure in the subclavian vein at
the opening of the thoracic duct is of importance for the flow of lyniph,
is shown by the fact that, if the pressure here is raised in any way, as by
ligature of the vein, the flow of lymph is entirely stopped, and there
may be a reflux of blood from the vein into the duct.

The work of Ludwig and his pupils has revealed to us the existence
of certain anatomical arrangements for furthering the flow of lymph.
Thus, in all tendons and aponeuroses of the body, we find a double
system of lymphatics, consisting of a deep network of capillaries with
meshes elongated in the direction of the fibrous bundles, and lying
directly on the muscular fibres ; and a superficial network with polygonal
meshes lying in the peritendinous connective tissue.^ Both networks
are in connection by means of small vertical branches, and contain no
valves. It is found that the slightest pressure or stretching of the
aponeuroses causes a flow of lymph from the deep into the superficial
meshwork, and from here into larger lymphatic vessels, which pass
through the substance of the muscles to join the large lymphatic
trunks. A very similar arrangement of lymphatics has been described
by Ludwig and Schweigger-Seidel,^ in the central tendon of the
diaphragm. These may be injected by introducing some coloured fluid
into the abdominal cavity of a freshly-killed animal, and then carrying
out artificial respiratory movements.

The physiological proof of these deductions from anatomical obser-
vations was furnished Ijy Genersich,* who showed that the lymph flow

^ Gaslcell, Arh. a. d. physlol. And. zu Leip~dg, 1876.

^ "Die Lyni[)ligefiissc der Fascien mid Sehnen," Leipzig, 1872.

" Arl. a. d. fhyHiol. Ansl. r.u Leipziri, 1866. * Ibid., 1870,



FOR CES CONCERNED IN MO VEiMENT OF L YMPH. 301

could be largely increased by passive flexion and extension of the limbs.
We must therefore look upon the entire muscular system as one of
the chief sources of the energy for maintaining the lymphatic circula-
tion, especially as the presence of valves in the lymphatics converts
every nmscular contraction which may press on the vessels into a
driving force.

We have finally to consider the effect of changes in the calibre of
the lymphatics themselves on the onward flow of lymph. In the frog
(and in other amphibia, and also in Saitropsida) the lymph circulation
is maintained by special contractile cavities called lymph hearts, situated
in pairs, an anterior pair beneath the scapulse, and a posterior pair in
the ileo-coccygeal space.

The chief points with regard to the normal anatomy and physiology of the
batrachian lymph hearts have been simimed up as follows, by J. Priestley : ^ —

1. The hearts are muscular sacs, the fibres of which branch and freely
anastomose and are transversely striated. Their walls are penetrated by
medullated and non-meduUated nerve fibres, and small nerve ganglia are
situated in the neighbourhood of the hearts, but no ganglion cells
have as yet been recognised amidst the muscular fibres. They collect the
lymph from more or less extensive lymphatic regions, and force it past valves
into large veins, the anterior pair of hearts into branches of the jugular, the
posterior pair into branches of the ischiatic vein. They are suppHed by
nerves from the spinal cord, the anterior pair by the second, the posterior pair
by the tenth spinal nerve.

2. The hearts exhibit throughout life a pulsation with a mean rate of
sixty to seventy a minute. It is, however, not continuously regular, being
interrupted by pauses, and by periods of great acceleration. The pauses some-
times follow movements on the part of the animal, but often they cannot be
set down to any definite cause. After such pauses the pulsations begin as
twitches before falling into beats of normal fulness. The periods of acceleration
also seem to be determined, for the most part, by movements of the animal.

3. The hearts are governed by cerebro-spinal centres — motor and inhibitory.
The motor centres are situated in the spinal cord, those for the anterior pair
opposite the third, and those for the posterior pair opposite the sixth
vertebra. They transmit their impulses down the appropriate spinal nerves
of their own side of the body ; and each is independent of the rest. They
originate the normal rhythm of the hearts ; and their action, whatever its exact
nature, is automatic, or not due directly to afferent stimuli ; hence no change
in the lymph current traversing the hearts can alter their rhythm. The
inhibitory centre is situated in the encephalon, in the optic lobes ; it is
constantly in action.

4. These centres are in connection with afferent nerves. Strong stimuli,
applied to the blood heart or to the abdominal viscera, lead to inhibition of the
heart beats, if the upper centre is intact ; while strong sensory stimuli applied
to the skin may inhibit the lymph hearts whether the u|)per centre is
present or not.

5. But though governed by the above centres, the lymph hearts seem
capable of an irregular pulsation when separated from them. Such pidsation
consists of flickers and indefinite confused twitchings for the most part,
which, when the heart is vigorous, harmonise occasionally to full beats. The
nature of these movements is still doubtful. The most that can be said about
them is that they are probably not solely muscular, since curari abolishes them.

^ Jouom. Physiol., Cambridge and London, 1879, vol. i. p. 1. Cf. also the account by v.
Witticli in Hermann's " Handbuch," Bd. v. (2) S. 325, where full references to the liter-
ature of the subject are given.



302 PROD UCTION AND ABSORPTION OF L YMPH.

Xo such meclmnism exists in the mammaha. Heller and Colin
have observed rhythmic contractions of the lacteals in the mesentery,
but only m the herbivora. In the case of the chyle vessels, Biiicke ^ has
shown that the onward flow of lymph is helped by the rhythmic con-
tractions of the muscular fibres of the intestinal vilh, which empty the
central cavity of the villus into the underlying network of lymphatics.

Since the walls of most lymphatic vessels and of the thoracic duct
are provided with unstriated muscular fil^res, we should expect these
vessels to be constricted, in consequence of direct stimulation, and such
constrictions have been observed in executed criminals. It has been
shown more recently that an active contraction or dilatation of the
lymphatics can be brought about by electrical stimulation of certain
nerves. Thus Paul Bert and Laffont^ noticed contraction of the
lacteals on stimulation of the mesenteric nerves, and a dilatation of the
same vessels on exciting the splanchnics. Grley and Camus ^ have
lately repeated these experiments more carefully, and have obtained
graphic evidence of a dilatation of the cisterna lymphatica on stimula-
tion of the splanchnic nerve. This dilatation of the cisterna probably
explains the temporary stoppage in the lymph flow from the thoracic
duct wdiich I described as the immediate effect of splanchnic stimulation.

It is probable, however, that the active contractility of the walls of
the lymphatics is of very little importance for the flow of lymph
through them. The only factors which are of importance are mechanical,
and are —

1. The pressure under which the lymph is poured into the tissue
spaces. This in its turn is dependent on the differences of pressure
between the intra- and extracapillary fluids, as well as on the per-
meabihty of the vessel walls.

2. All the muscular contractions of the" body, and especially those
by which the respiratory movements are carried out.

The Absorption of Lymph from the Connective Tissues.

Relative importance of blood vessels and lymphatics. — Before
the discovery of the lacteals by Aselhus, anatomists ascribed the office
of absorption generally to the veins. From this time until the begin-
ning of the present century, no subject was more hotly disputed than
the question of the relative importance of the veins and of lymphatics
in the processes of absorption.

It was generally conceded that the lacteals performed practically
the whole work of absorbing the products of digestion from the intes-
tines ; but the views as to the functions of the other lymphatics of the
body were many and various. Thus, when Nuck * first made his
experiments, in which he thought he injected these lymphatics from the
arteries, he concluded that they had no other use than as correspondent
veins, to return the lymph from such arteries as were too small to admit
the red blood corpuscles. As anatomical and clinical knowledge increased,
it was gradually recognised that the general lymphatics of the body had
a function similar to that of the lacteals in the intestines, and like them

^ "Ueber die Chylusgefasse uud Fortbevvegung des Cliylus," Wien, 1853.

- Compt. rend. Acad. d. sc, Paris, March 13, 1872.

2 "Piecherches dans les causes de la circulation lyniphatique," Diss., Paris, 1894.

* " Adenograpliia curiosa, ■' Leidai, 1691.



ABSORPTION FROM CONNECTIVE TISSUES. 303

were able to absorb fluids as well as solids in fine suspension or solution.
A number of reasons for this conclusion are given by Johannes Mtiller,
and I may quote some of these as an example of the arguments by
which older anatomists, such as Hunter and Hewson, had come to hold
this opinion. In the first place, the lymphatics often become painful,
red streaks appear in their course, and the neighbouring lymphatic
glands become swollen after the application by friction of irritating
matters to the skin. Mascagni asserted that, in animals which died
from pulmonary or abdominal htemorrhage, the lymphatics of the pleura
and peritoneum were filled with blood (Mtiller discredits this assertion as
" extravagant "). Mascagni and Soemmering observed bile in the
lymphatics coming from the liver, in cases where the bile ducts were
obstructed. Tiedemann and G-melin,^ after tying the ductus choledo-
chus in dogs, found the lymphatics of the liver filled with a fluid of a deep
yellow colour. The lymphatic glands through which these lymphatics
passed were yellow, and the yellow fluid taken from the thoracic duct con-
tained biliary constituents. The effect of this and similar evidence on the
minds of the anatomists in Hunter's time was rather curious. Since
nature had provided a system — the lymphatics — on purpose to serve
the office of absorption, it was considered in the highest degree
improbable that this office would also be carried out by the veins, and
William and John Hunter, as the result of experiments on absorption
from the intestines, concluded that the veins take no part in absorption.
To this view of exclusive power of absorption possessed by the
lymphatics, it was objected that animals exist which possess neither
lacteals nor lymphatics. It was therefore regarded as a brilliant victory
for the hypothesis, when Hewson demonstrated the existence of lacteal
and lymphatic vessels in birds, reptiles, and fishes.

Subsequent researches, especially by Magendie,^ have shown, how-
ever, that absorption from all parts of the body can be effected by
blood vessels as well as by lymphatics. Magendie's researches have
been continued and extended of late years by Ascher ^ in the case of
the connective tissues of the lower limbs, by Tubby and myself * in the
case of the pleural and peritoneal cavities. We found, for example,
that, after injecting methylene-blue or indigo -carmine into the pleura,
the dye-stuff appeared in the urine within five minutes, whereas the
lymph presented no trace of blue for another twenty minutes, or even
two hours. It is evident that in this case the dye must have been
taken up by the blood vessels and not by the lymphatics, and that
this vascular absorption takes place with extreme rapidity. In a later
series of experiments, Leathes^ has shown that, after introduction of
various salt solutions into the serous cavities, an interchange of con-
stituents takes place directly between the blood and the injected fluid,
so that the latter in a very short time becomes isotonic with the blood
plasma. Now, in this mode of absorption by the blood vessels the so-
called absorption really consists in an interchange between blood and
extravascular fluids — an interchange apparently dependent entirely
upon processes of diffusion between these two fluids. So long as any

^ Quoted by Mtiller (Baly's translation, vol. i. p. 242).

^ Precis elementaire de physiologie, " Paris, 1836.

^ Ztschr.f. Biol., Miinchen, 1893, Bd. xxix. S. 247.

^ Journ. Phydol., Cambridge and London, 1894, vol. xvi. p. 140.

^^ Ibid., 1895, vol. xviii. p. 106.



3 04 PROD UCTIOAT AND ABSORPTION OF L YMPH.

difl'erence in composition exists between intra- and extravascular fluids,
so long will diffusion currents be set up tending to equalise this
difference.

Absorption of isotonic fluids. — These experiments, therefore, have
no direct bearing on the absorption of lymph, i.e. the normal tissue
juices. In this case the fluid to be absorbed resembles in almost all
particulars the blood plasma, and possesses the same osmotic pressure
as the latter, so that it would seem that there are no forces of diffusion
or osmosis tending to absorption. Miiller^ concludes from similar
considerations that " the removal of collections of fluid must be effected
in many cases by means of the lymphatics, independently of imbibi-
tion into the capillaries." The mechanism of this lymphatic absorption
has been already studied. We have now to inquire whether at any
time fluids, such as those normally present in the tissues and isotonic
with the blood, can be taken up by the blood vessels.

We may arrange the experiments which have been made to decide
this point under three headings —

1. In the first set, observations were made on the absorption of
isotonic salt solutions and blood serum from the pleural and peritoneal
cavities. Orlow,^ working under Heidenhain's direction, found that
such fluids were absorbed rapidly from the peritoneal cavities of living
animals, wliile the lymph flow from a cannula placed in the thoracic
duct showed no (or only sUght) increase, in no way comparable to
the amount of fluid absorbed. He concluded, therefore, that the
absorption was effected by the blood vessels and was dependent on
the vital activity of the cells lining the serous cavities or of the



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 42 of 147)