III. Deficient oxygenation of blood interfering with the normal
metamorphosis of bile.
IV. Excessive secretion of bile, more of which is absorbed than can
undergo the normal metamorphosis.
Congestion of the liver: _a._ Mechanical, _b._ Active, _c._ Passive.
V. Undue absorption of bile into the blood from habitual or protracted
constipation.
Mechanical obstruction, by tying the bile ducts in a dog, caused in two
hours yellow coloration of the contents of the hepatic lymphatics and
thoracic duct, and also of the blood in the hepatic veins (Saunders).
That this jaundice is due to reabsorption and not to suppressed
secretion of bile, already present in the blood, may be fairly inferred,
from the complete absence of icterus, where, from general disease of the
liver, the secretion of bile has been entirely suspended, and in which
the gall ducts and bladder contain only a little gray mucus (Haspell,
Frerichs, Budd, Murchison), also from the fact that after complete
extirpation of the liver in frogs not a trace of biliary acids nor
pigment can be detected in the blood, urine, or muscular tissue (Müller,
Runde, Lehmann, Moleschott). Bile acids and bile pigment are formed in
the liver by disintegration of blood globules, and when present in
excess in the blood it is by virtue of reabsorption.
This reabsorption will take place under the slightest favoring
influence. The obstructions in the bile duct, above referred to, cause
the tension in these ducts to exceed that of the blood in the
capillaries of the liver and at once osmosis of bile into the blood
vessels sets in. This may occur from so slight a cause as the congestion
and swelling of the duodenal mucosa around the opening of the bile duct.
Again reabsorption of bile may be determined by a lessening of the
normal fullness and tension of the hepatic capillaries as when the aorta
is mechanically compressed by abscess, neoplasm, ingesta, or otherwise,
just behind the diaphragm (Heidenham, Brunton). The cause is the same in
both cases, namely, the want of balance between the fullness and tension
of the bile ducts, and the hepatic blood vessels. There is increased
fullness of the hepatic biliary ducts, or decreased plenitude of the
hepatic capillaries and lymphatics.
It must be added, however, that the coloring matter of the bile is
apparently produced, in the liver, from that of the blood, and that the
pigment (hæmatoidin), found in old extravasations of blood, is probably
identical with bilirubin, and that any agent or condition which causes
liberation of the coloring matter of the red blood globules, will cause
a staining of the tissues, like that of jaundice. The following agents
are known to have this effect on the blood globules: water, in hydroæmic
states of the blood (Hermann); taurocholate of soda from absorption of
bile (Frerichs, Kuhne, Feltz, Ritter); chloroform (Chaumont); ether
(Burdon-Sanderson); freezing (Rollet); a high temperature +60° C.
(Schultze); frictional and induction currents of electricity
(Burdon-Sanderson); the alkalies (ammonia, potash and soda) and nitrites
when present in excess.
The injection of hæmoglobin into the veins of dogs has been followed by
the appearance of bile pigment in the urine, but Naumyn, Wolff, Legg and
Brunton failed to obtain the same result in rabbits.
It is noticeable that the hæmoglobin of horses’ blood is very soluble at
all temperatures and that of dogs very slightly so (Burdon-Sanderson).
This may serve to explain the great prevalence among solipeds of
diseases, associated with dusky brown or yellow discoloration of the
mucosæ, with petechiæ, and with the passage of blood pigments in the
urine. It may further explain the usually benignant course of jaundice
in the horse and its extreme gravity in the dog.
There is further reason to believe that the bile acids, when in excess,
may be transformed into bile pigment in certain conditions of the blood,
as occurs under the action of sulphuric acid out of the body (Stœdler,
Meukomen, Folwarcyny, Röhrig). Moreover, in the healthy state, the
greater part of the bile secreted, including acids and pigment, is
re-absorbed from the intestinal canal, but is oxidized and decomposed in
the blood so that it cannot be detected, in blood or urine. But let the
transformation be interrupted, as in certain diseases of the lungs, with
imperfect oxidation, and the bile circulates in the blood, stains
tissues and urine, and in short causes jaundice.
To sum up: it may be said that icterus is probably never due to simple
inactivity of the liver: it may, however, be caused by excessive
secretion of bile which is re-absorbed from obstructed bile ducts or
bowels:—it may result from imperfect transformation, in the blood, of
the bile which is normally re-absorbed from the intestine: or it may
possibly be caused by the formation of pigments in the blood from the
abnormal transformation of bile acids, or by solution of the hæmoglobin
of the blood corpuscles.
The gravity of jaundice varies as much as its causes. It is well known
that the system may be saturated with bile, and the tissues and urine
deeply stained without much constitutional disorder. The pigment alone
is not an active poison. But there may be much attendant suffering from
obstructed biliary ducts or bowels, from diseases of the lungs, or from
disintegration of the blood globules and imperfect nutrition, or there
may be profound nervous prostration and disorder from uræmia, or from
the presence in the blood of an excess of effete and partially oxidized
albuminoids (See Azotæmia). According to our present knowledge,
constitutional disorder, prostration and suffering in cases of jaundice,
are mainly due to the presence in the circulation of these albuminoids,
and of taurocholic acid which latter has a most destructive effect on
the blood corpuscles.
The _symptoms_, therefore, are not characteristic apart from the yellow
coloration of the tissues and urine and the chemical reactions of the
bile acids and bile pigments furnished by the latter.
The coloration of the tissues may be a simple tinge of yellow especially
noticeable in the eye (conjunctiva), or it may amount to the darkest
shades of orange and brown. It may or may not be complicated by the
presence of spots or patches of blood-staining (ecchymosis) on the
visible mucous membranes but especially in cases complicated by
poisoning with taurocholic acid or effete nitrogenous products.
The urine may be similarly colored in all shades of yellow or orange
brown, and may leave a correspondingly deep stain on white paper.
The _test_ for _bile pigments_ (Gmelin’s) is simple and beautiful. Pour
a little nitric acid into a test tube held obliquely and then add a few
drops of sulphuric acid, and finally a little urine, so slowly, that it
will remain on the surface. Soon at the point of junction appear in
succession the various colors of the rainbow: yellow, green, blue,
violet, red and lastly a dirty yellow. It is open to this objection that
the characteristic play of colors may be produced by alcohol in the
absence of bile pigments. Indican also will produce the green and yellow
with blue between but never the violet nor red, nor all in their regular
order.
A _second mode_ of applying this test is by spreading a few drops of the
urine on a white plate and letting fall a drop of nitric acid in the
centre. The play of colors is very characteristic.
The _test for bile acids_ (Pettenkofer’s) is to place a portion of the
urine in a test tube, and after adding a drop of syrup, to add
cautiously, drop by drop, two-thirds of the amount of sulphuric acid.
Shake the mixture and set aside for some minutes. If sufficient heat is
not produced by the mixing of the acid and urine warm slightly. The
mixture becomes of a dark violet color which is destroyed by a
temperature a little above 140° Fah.
A convenient application of this test (Stranburg) is to add a little
cane sugar to the urine, dip a piece of filtering paper in the mixture,
dry it thoroughly, pour a drop of sulphuric acid on the paper and allow
it to run partially off. In a quarter of a minute a beautiful violet
color is produced, best seen by holding up the paper to the light and
looking through it (Brunton).
In cases due to obstruction of the bile ducts the dung is destitute of
bile, whitish, often clayey and fœtid, while in cases due to
reabsorption without obstruction the fæces have their natural color and
odor.
It is needless to enumerate all the concomitant symptoms of jaundice
which will be better noticed under the different disorders which
determine it, for a list of which see the _causes_.
The gravity of the affection will depend on the dangerous nature of
these concurrent diseases, and the destructive changes in the liver and
blood rather than on the depth of color in the textures.