_Causes._ Beside the general causes above mentioned, may be specially
named, musty, decomposed, and irritant fodders: those which like green
legumes, are easily fermented; and those which contain stimulating
volatile oils or carminative principles. They are also especially
exposed to such causes as severe and prolonged work under a hot sun, the
nervous atony which causes vaso-dilatation in a hot climate, and such
traumatisms as come from falls, kicks, goring, and blows by shafts,
poles and clubs. These especially induce _active congestion_. The
_passive_ forms come mainly from obstruction in the lungs, or heart
(dilatation, right valvular insufficiency, pericarditis,
hydropericardium, myocarditis, fatty degeneration, endocarditis), or in
the posterior vena cava.
_Lesions._ The congested liver is enlarged and deeply colored with
blood. The weight of twenty to thirty pounds is often attained. While
the color is of a deep red throughout, there are spots of a still darker
hue indicating the seat of subcapsular or deeper seated hemorrhages. The
color varies according as the congestion is passive or active. In the
former the coloration is deeper in the centre of the acinus (nutmeg
liver) indicating congestion of the hepatic veins, while in the latter
the periphery of the acinus may be most deeply stained implying
congestion of the portal vein. The consistency of the organ is
diminished, and the more acute the attack the greater the friability. In
such cases there is a parboiled appearance indicating granular and
commencing fatty degeneration. Under the microscope the relative
distension of the intralobular, and interlobular veins and the hepatic
capillaries becomes more distinctly marked and the presence of pigment
and fatty granules and the lack of protoplasm and nuclei in the hepatic
cells indicate their progressive changes. When the peripheral cells are
pale from fatty granules the contrast between the light margin and dark
centre of the acinus, makes the mottled or nutmeg aspect of the liver
much more pronounced.
In old standing cases of passive congestion the liver may be the seat of
fibroid degeneration, extending from the capsule inward in bands or
trabeculæ, and giving to the organ a firm resistant character
(sclerosis, cirrhosis).
_Symptoms._ The symptoms are general and suggestive rather than
pathognomonic. There are dullness, prostration, unsteady walk, pendent
head, with occasional jerking, semi-closed eyes, redness of the
conjunctiva, slight colicy pains, arching of the loins, muscular
tremblings and decubitus on the left side rather than the right. The
more definite symptoms are tenderness on percussion with the closed fist
over the last ribs (the liver) especially on the right side, increase of
the area of hepatic percussion dullness (which may be rendered valueless
by a loaded colon), the presence of a slight icterus in the conjunctiva
and urine, and an increase of the urine secreted and an excess of the
contained urea.
In _passive_ cases however the obstruction to the escape of blood from
the liver prevents the development of icteric symptoms, of uræmia and of
polyuria. In all such cases however there follows a general congestion
of the portal system and if it persists for any length of time
gastro-intestinal congestion and catarrh and even ascites may develop.
In all cases alike the history of the attack will help towards a
satisfactory diagnosis.
_Prevention._ A rational hygiene embracing daily work or exercise,
moderate laxative diet, green food in its season, pure cool air are
important precautions.
_Treatment._ A moderate supply of green or laxative food, the
withholding for the time of grain, and especially of maize, wheat or
buckwheat, saline laxatives daily, and a stimulating embrocation or
blister to the tender hypochondrium are the most important measures.
Exercise in a box stall, or still better in a yard or paddock in the
intervals between more systematic work forms an important adjunct to
medicine. As a laxative sulphate of soda is to be preferred at first in
a full cathartic dose and later in a daily amount sufficient to relax
the bowels. Given in a bucket of water every morning before the first
meal a very small dose will be effective.