place when the structure of the organ affected is such that the
admission of arterial blood is wholly interfered with. This is the
case in the heart and kidneys, and to a less extent in the spleen. The
opportunity is presented for the diffusion of a fibrinogenous fluid,
lymph or blood-serum, through the cells of the organ which contains
the other essentials for coagulation, and the dead part presents the
characteristics attributed by Weigert[24] to death from clotting of
the protoplasm, coagulative or ischæmic necrosis.
[Footnote 24: _Ibid._, 1880, lxxix. 87.]
Embolism of the cerebral arteries produces softening of the brain, not
a hemorrhagic infarction or a yellowish necrosis. Weigert attributes
this result, on the one hand, to the absence in the brain of abundant
cells from which are to be had the ferment and fibrino-plastic
material necessary for coagulation, and, on the other, to the closure
of the spaces into which blood might collect by the rapid swelling of
the tissues from the exuded lymph.
The hemorrhagic results of embolism are also met with in obstruction
of branches of the mesenteric artery, which is considered by Litten,
at least from its function and in connection with its sluggish
current, to correspond with a terminal artery.
If the patient outlives these more mechanical results of embolism, the
local changes taking place are those tending to remove the
extravasated blood or the dead tissues. The embolus has become an
obstructing thrombus, and its removal is accomplished in the manner
already stated in connection with the subject of thrombosis. The
wedge-shaped nodule of hemorrhagic infarction becomes decolorized
through the absorption, in part, of the blood-pigment. That portion
which is not absorbed remains at the site of the original lesion as
granular or crystalline blood-pigment. A granulation-tissue is formed
at the periphery, which extends into the infarcted region, very much
as the endothelial and vascularized growth extends into a thrombus.
Eventually, a patch of cicatricial tissue remains as the sole
indication of the previous disturbance. This termination is rather
suggested for the hemorrhagic infarctions of the lungs. The results
are more apparent and more easily demonstrated in the case of the
anæmic necroses, and the somewhat irregular depressions with
wedge-shaped scars, seen upon the surface of the spleen or kidneys,
call attention to the probable nature of the process giving rise to
these results. A source of embolism must also be associated, that
these scars may be regarded as of embolic origin. The embolic
softenings of the brain are likewise represented in after years by
losses of substance. The superficial, yellow patches or localized
oedematous blebs, with corresponding atrophy of the convolutions
beneath, call attention to a nutritive disturbance, as do cyst-like
cavities in the deeper parts of the brain. Here, too, a source of
embolism must be found, that {66} the local destruction of tissue may
be attributed to embolic obstruction of vascular territories.
When the embolus arises from a septic thrombus, the results differ
from those above described. The embolus then carries not only
mechanical possibilities, but also a virulent action. The latter is
manifested by the rapid production of local inflammatory disturbances,
as circumscribed abscesses and gangrenous destruction of tissue. Since
emboli are frequently lodged near the surfaces of organs, a septic
pleurisy, pericarditis, or peritonitis is the usual result of the
dissemination of the virus contained in the embolus. This virus is
similar in character to that found in septic softening of the
thrombus, and, like it, is intimately connected with the presence of
microbia. Whether the latter are specific in character, as maintained
by Klebs and others, or whether they are to be included among those
associated with putrefactive processes, still remains an open
question.
The symptoms of thrombosis obviously depend upon the resulting
obstruction to the circulation of blood, and in the case of primitive
thrombi are gradual in their occurrence. The degree of mechanical
obstruction is determined by the nature of the thrombus, whether
parietal or obstructing, and by that of the vessel, whether provided
with anastomoses sufficient to permit a compensatory collateral
circulation or not. In the former case, if the thrombus is small and
deep-seated, there may be no symptoms to indicate its presence. When
the collateral circulation is insufficient to remove the blood from a
region whose efferent venous trunk is completely filled with a
thrombus, the phenomena of stagnation are produced. The part becomes
oedematous, and red blood-corpuscles escape from the distended vessel.
If the obstructed vein is superficial, the seat of the thrombus is
indicated by the resistance and sensitiveness of the part.
Characteristic disturbances of function are associated with thrombosis
of the various organs of the body. If the cerebral sinuses are
affected, mental disturbances arise; if a cardiac thrombosis is
present, it is frequently accompanied by irregularity and feebleness
of the heart. When the portal and renal veins are obstructed,
functional disturbances arise in the parts from which they receive
their blood.
The symptoms of embolism, like those of arterial thrombosis, are
primarily due to anæmia. Suddenness is their characteristic in
embolism, while they are gradual and progressive in the case of
thrombosis. An embolic anæmia is complete or incomplete according to
the terminal or anastomosing character of the obstructed vessel. The
effect of the anæmia is to stop or check the function of the part, and
varies according to the size and situation of the vessel. Hemiplegia,
or perhaps aphasia or other evidence of localized disturbance, follows
central embolism; angina pectoris, with a disturbed cardiac action,
results from embolism of the coronary artery. Sudden suffocative
symptoms, with open air-passages, suggest embolism of the larger
branches of the pulmonary artery. A considerable hæmaturia often
excites suspicion of an embolism of the renal artery, the hemorrhage
coming from the vessels in the neighborhood of the obstructed region.
Embolism of a large artery of an extremity is often localized by the
sensation of a blow at the part, to be followed by absent pulsation,
pallor, and coldness of the region beyond the place of obstruction.
{67} The symptoms of the subsequent effects of thrombosis and embolism
are to be inferred from what has already been stated with regard to
the nature of the possible lesions. To enter into their detailed
consideration would demand more space than is permitted, and would
modify an established sequence or necessitate a repetition, which is
undesirable in a systematic treatise.
Effusions.
The various fluids of the body are derived from without, and admitted
into the blood-vessels. The physiological transudation through the
walls of these vessels, in the main modified serum, becomes lymph as
it appears in the several lymph-spaces. From the latter the transuded
fluid either returns through the lymph-vessels to the blood-current or
makes its appearance upon surfaces as secretions. These are variously
modified as they pass through the specific cells of glands or as they
are met with in the several closed cavities of the body.
The transudations thus occurring may vary in quantity within certain
limits, the latter being somewhat indefinite, owing to the
difficulties in the way of exactly measuring the fluid transuded. The
greater part of this transudation is represented by the quantity of
lymph flowing through the main lymph-trunk, and of the secretion from
the glandular surfaces of a given region of the body; but that
transuded fluid is not included which may return to the blood-vessels
without being carried into the general lymph-current or secreted from
a gland. Such a direct return may be considered to take place whenever
the pressure upon the outside of the vessel wall is greater than that
within the latter, or when the chemical composition of the fluids on
the two sides of the filter permits endosmosis as well as exosmosis.
This varying relation in the direction of the current through the
vessel wall is likely to be of frequent, if not constant, occurrence
in connection with the physiological processes taking place throughout
the body.
The undue accumulation of the transudation in the various closed
cavities of the body is known as dropsy, and the fluid present is
regarded as an effusion or an exudation. These terms are often applied
somewhat vaguely, now being used as synonymous, again as representing
different conditions of the transudation, which are attributed to the
varying conditions of its accumulation.
Exudation is more generally used when an inflammatory process is the
cause of the increased transudation, while effusion is more strictly
associated with causes other than inflammatory. In the present
consideration this etiological distinction will be maintained.
To appreciate the conditions under which pathological accumulations of
fluid, whether effusions or exudations, may arise, it is desirable to
bear in mind the essential conditions which prevail in the occurrence
of transudation, since the former are likewise chiefly derived from
the blood and are transuded through the walls of its vessels. These
conditions are largely dependent upon the laws governing the diffusion
of substances through an animal membrane, the vascular wall
representing the filter. As a living membrane its relation is
dependent upon vital as well as {68} physical conditions, and the
former produce certain important modifications in the physical process
of filtration.
The transudation through the vessels takes place chiefly through those
with the thinnest walls, the capillaries, although it is probable that
a certain degree of transudation may also occur through the walls of
the smallest veins. The causes which are instrumental in promoting the
circulation of the blood--viz. the contraction and dilatation of the
heart, the contraction of the arteries, the inspiratory action of the
thorax, and muscular movements throughout the body--are also essential
in producing the flow of lymph; and the existence of pressure upon the
hæmic side of the filter is the first feature of importance in
occasioning the transudation. The constant removal of the transudation
from the outer side results from the pressure being less in this
position.
At the same time, an increase in the quantity of blood in the vessels
is not necessarily productive of any considerable increase in the
fluid transuded. Cohnheim calls attention to the experiments of Worm
Müller, which show that a plethoric condition may readily be produced
by the injection of quantities of blood into the circulation of
animals, the amount of which cannot exceed twice the volume of the
animal's blood without producing death. Although a temporary increase
of the blood-pressure results, a return to the normal quickly follows.
This is permitted by the propulsion of the excess of blood into the
capillaries and veins, which become consequently distended, especially
those of the abdominal organs. There is no increased transudation
corresponding with the quantity of fluid introduced, nor is there any
considerable distension of the blood-vessels of the skin, subcutaneous
or intermuscular connective tissue. Such experiments show no permanent
increase in the blood-pressure within the large veins if there is no
obstruction to the admission of venous blood into the heart,
presumably owing to their capacity for considerable distension.
Although experiments show that a simple plethora with great distension
of the capillaries of the abdominal organs occasions no considerable
increase of transudation, a different result follows a hydræmic
plethora[25] induced by the injection of immense quantities of salt
water into the blood-current--often six times as much liquid as the
animal had blood. Here, too, the arterial blood-pressure shows no
permanent increase, nor does that within the large veins become
perceptibly increased till enormous quantities of fluid are injected.
The blood flows through the vessels with increased rapidity in
consequence of the diminished friction of the diluted blood, and an
increased transudation begins at once. The various glands, salivary
and gastro-intestinal, kidneys and liver, secrete more copiously, and
the flow of a dilute lymph from the thoracic duct becomes greatly
increased, while that from the cervical lymphatics becomes moderately
accelerated. The lymph from the extremities, however, is no greater in
quantity than that flowing from an animal in a perfectly normal
condition. The localization of the increased transudation from the
blood-vessels is further characterized by the abundant accumulation of
watery fluid in all the abdominal organs and abdominal cavity, in the
salivary glands and surrounding connective tissue, while elsewhere in
the body the organs and tissues are almost invariably in the same
condition with {69} regard to moisture as are those of a healthy
animal under normal circumstances.
[Footnote 25: Cohnheim and Lichtheim, _Virchow's Archiv_, 1877, lxix.
106.]
The importance of these experiments with reference to the causes of
the transudation of fluid from the blood is obvious. The pressure upon
the walls of the blood-vessels cannot become sufficiently increased to
be accompanied with augmented transudation until limits are reached
which are beyond the possibilities of occurrence in the human body.
When such limits are attained in animals, the increased pressure,
however great it may be, does not suffice to produce a general
transudation, but one limited to the vessels of those parts of the
body whose normal function is connected with too abundant transudation
of fluid. A simple hydræmic condition of brief duration has been
proven, by experiment, insufficient to give rise to increased
transudation, neither increased secretion nor increased flow of lymph
taking place. The inference from these experiments is that an
increased transudation is more dependent upon conditions of the filter
than upon those of blood-pressure. The absence of any observable
changes in the filter leads to the assumption of an increased
permeability, of physiological occurrence in certain parts of the
body, as the chief feature in the occurrence of increased
transudations.
Dropsy arises when the transudation is accumulated. As dropsical
accumulations are transudations from the blood, essentially
blood-serum with a diminished percentage of albumen, and as such
blood-serum is practically lymph from its presence in the
lymph-vessels, dropsical effusions are to be regarded as stagnant
lymph. Such stagnations may be present in the small lymph-spaces
within the connective tissue, or in the larger lymph-sacs, as the
peritoneal, pleural, pericardial, and scrotal cavities. In like
manner, the stagnation may take place in the cavities of joints and in
those of the brain and cord, although the latter represent functional
rather than structural lymph-canals.
The term oedema is applied to the accumulation in the
connective-tissue lymph-spaces in general, while the term anasarca is
confined to those cases where the subcutaneous lymph-spaces are
concerned. The accumulation in the great lymph-cavities is known as
ascites when peritoneal, hydrothorax when pleural, hydropericardium
when pericardial, hydrocele when in the cavity of the tunica
vaginalis, hydrocephalus if within the ventricles of the brain, and
hydromyelocele when within the central canal of the spinal cord.
The accumulation of dropsical effusions may be considered as possibly
resulting from an obstruction to the channels through which the
transudation should flow, or from insufficient force to overcome
normal obstructions, or from an abnormally increased transudation.
Lymph-channels are frequently obstructed, but no appreciable diffused
retention of lymph results unless the thoracic duct is obstructed.
This rare affection is followed by enormous distension of the thoracic
and abdominal portions of the parts beyond the stenosis. Ascites and
hydrothorax may follow, but not necessarily any considerable oedema of
the peripheral parts of the body. As a result of the distension of the
thoracic duct, rupture is not unlikely to take place, and the effused
fluid contains chyle.[26]
[Footnote 26: Quincke, _Deutsches Archiv für Klin. Med._, 1875, xvi.
121.]
{70} That the obstruction is not followed by oedema is attributable to
the innumerable anastomoses between the lymph-spaces, and also to the
probability that a part of the transuded fluid returns to the
blood-vessels when the obstruction is impassable.
The forces necessary to promote the flow of lymph have already been
mentioned, and their entire removal is inconsistent with life. A
diminution of their activity is more likely to result in a diminished
flow of lymph than its accumulation, although a slowing of the
lymph-current may represent a favoring element in the accumulation of
an increased transudation.
The occurrence of dropsy with unobstructed lymph-channels, and in the
presence of efficient agencies in promoting the flow of lymph,
indicates the importance of an increased transudation as the chief
element in the occurrence of a dropsical accumulation. An increased
transudation, with resulting oedema, is readily produced by preventing
the flow of blood from a part, and may be directly observed with the
microscope. Cohnheim states that after a sudden venous obstruction, in
case an efficient collateral circulation does not interfere, the
capillaries and small veins become distended with stagnant blood and
appear as masses of red blood-corpuscles. This distension results from
the continuance of the arterial flow into the capillaries of the
obstructed region under a pressure which is only neutralized by the
resistance of the tissues and the transudation from the capillaries.
Sotnitschewsky[27] shows that a concurrent paralysis of the vaso-motor
nerves, as claimed by Ranvier, is unnecessary. The transudation
through the capillary wall is increased, the flow of lymph from the
part is accelerated, and oedema arises when the transudation is so
much augmented that the calibre of the lymph-vessels is insufficient
for its removal; and the greater this insufficiency the greater is the
oedema. With the continuance of the arterial flow and intravenous
resistance, red blood-corpuscles are forced through the filter, and
form an important constituent of the effusion from venous stagnation.
[Footnote 27: _Virchow's Archiv_, 1879, lxxvii. 85.]
Although the existence of an increased pressure upon the capillary
wall is obvious from the experiment referred to, there is no increased
arterial pressure--rather a diminution--and the important element in
occasioning the increased permeability of the capillary wall is the
obstruction to the outflow of venous blood from the oedematous region.
In consequence of the latter the arterial flow is followed by
increased transudation.
Dropsies resulting from venous obstruction, as well as those following
an obstruction of the thoracic duct or its branches, or of the several
lymphatics of a part, are classified as mechanical dropsies. That from
venous obstruction is the most frequent, and its seat may lie in the
course of venous trunks or in the heart, lungs, or liver. The venous
obstruction must be so situated that the stagnant blood is unable to
find a ready escape through collateral branches. The more sudden and
complete it is, the more likely is the effusion to contain
considerable numbers of red blood-corpuscles.
In addition to the element of venous stagnation in producing increased
transudation, the condition of the filter is of importance. The
occurrence of oedema in chronic diseases, especially of the kidneys,
and in those attended with protracted suppuration, continued
hemorrhage, and the {71} rapid growth of tumors, has usually been
attributed to the watery condition of the blood, with a diminution of
the albumen. Cohnheim, however, suggests that the condition of the
vessel wall is of more importance than the contents as the immediate
cause of the increased transudation. The more or less protracted
action of various agents--temperature, insufficient oxygen, and
diminished albumen--is likely to so modify the condition of the
endothelium as to favor an increased permeability of the wall.
Experiments show that a simple acute hydræmia produces no increased
transudation, and that a chronic hydræmia, if connected with dropsy,
is likely to be influential by increasing the permeability of the
wall. Even in those cases where a hydræmia and an oedema co-exist, the
localization of the latter is favored by obvious disturbances of the
function of the capillary walls, as in case of the cutaneous oedema
after scarlatina. In like manner, a feeble heart, favoring venous
stagnation, and gravitation are of importance, as general causes, in
promoting dropsy in hydræmic conditions.
The possibility of the occurrence of oedema through nervous influence
is not to be denied. The localized and fleeting oedema of urticaria
and erythema, the swollen lip and tongue in connection with digestive
disturbances, are not to be explained by the two main factors of
oedema--viz. venous stagnation and increased permeability of the
vascular walls. Cohnheim refers to the rapid occurrence of oedema of
the tongue as a result of irritation of the lingual nerve, and oedema
is known to occur rapidly in cases of acute myelitis. A similar result
follows the experimental destruction of the spinal cord, although the
mechanism of its production is not apparent.
Dropsies are subdivided, as regards their distribution, into general
and local forms. The causes producing the two varieties are
essentially those already described. The causes of all local dropsies
are not always to be regarded as the same. Regions which are the seat
of mechanical dropsies are often affected by inflammation, with
abundant serous exudation--the so-called inflammatory dropsy. The
properties of the effusion and exudation are quite different, the
former having a small percentage of albumen, but few leucocytes, with
a corresponding absence of fibrin, and few or many red
blood-corpuscles. The exudation, on the contrary, is highly
albuminous, though less so than the blood-plasma; it contains numerous
leucocytes and much fibrin; under ordinary circumstances there are but
few red blood-corpuscles.
The local dropsies are often characterized by special terms. Hydrops
ex vacuo is applied to the collections of fluid found in closed
cavities with unyielding walls, as the cranium and thorax, or to the
recurrence of fluid in cavities from which the same has been rapidly
removed, in the absence of inflammatory disturbances. Collateral
oedema is usually applied to the association of oedema with
inflammatory disturbances, and represents an extension of the
inflammatory process to the region concerned. Oedema of the glottis
and circumscribed oedema of the lung are instances. The term
hypostatic oedema is often used to designate the association of oedema
and inflammation, the former caused by the latter, and to indicate the
effect of gravitation in the localization of oedema from the general
causes already mentioned.