Physiologically after a meal is hyperæmic, and may increase one-third.
Rich feed and temporary idleness may cause morbid congestion. Other
causes are: ptomaines and toxins in spoiled food, hepatic irritants,
damp, hot, tropical climates, warm, damp, buildings, overfeeding,
dilated right heart, insufficiency of tricuspid valve, pulmonary
emphysema or congestion. Absence of valve between the right heart and
hepatic veins, slow hepatic circulation, dilatability of hepatic
vascular system, compression of lung by false membranes, œdema,
hepatization, infarction, hydrothorax. In horse: special causes:
spoiled fodders, carminatives, volatile oils, work in hot sun,
vaso-dilatation in heat and atony, falls, kicks, goring, blows;
passive forms from obstacles to the circulation. Lesions: Hepatic
enlargement to 20 or 30 pounds, and dark red color, darker spots of
extravasation, hepatic vein congestion in centre, and portal vein
congestion in periphery of acinus, softening, granular, fatty, nuclei
disappear from hepatic cells, nutmeg liver, cirrhosis. Symptoms:
general febrile symptoms, great prostration, drowsiness, slight
colics, arched loins, trembling or jerking, lies on right side,
percussion on last ribs painful, slight icterus and increased
urination and urea. In passive cases, less icterus and kidney trouble;
tends to intestinal catarrh and ascites. Prevention: good hygiene,
moderate laxative ration, cool air, exercise. Treatment: green or
laxative foods, salines, derivatives, water at will, always before
morning feed. In dog: overfeeding, indolence: pulmonary and
circulatory troubles. Lesions: nutmeg liver, degeneration, cirrhosis.
Symptoms: pampered idleness, obesity, pulmonary or cardiac disease,
intestinal catarrh, piles, ascites, slight icterus, percussion
tenderness of right hypochondrium, lying on right side, increase of
percussion flatness. Treatment: saline purgatives or laxatives,
antiseptics, restricted laxative diet, open air exercise, derivatives,
etc.
Physiologically the liver undergoes hyperæmia in connection with an
abundant meal and active digestion. Within the limits of health it may
increase one-third in bulk and weight. When this hyperæmia attends on
temporary idleness and rich feeding it may overstep the limits of health
and become pathological. Other causes of pathological congestion are,
tainted food rich in ptomaines and toxins, food injured by cryptogams,
and food that contains principles irritating to the liver. It is
especially common in swampy regions in tropical or semi-tropical
latitudes, and where the warm air is surcharged with moisture. Hot,
close, damp stables, with overfeeding and lack of exercise in the
pampered horse or dog, or under the forcing system of feeding for
exhibition, or for the butcher, acts in a similar manner. Dilatation of
the right heart, or imperfection of the tricuspid valve is a direct
cause of mechanical congestion and emphysema, congestion or other
obstruction in the lungs has a similar effect. In short the absence of
valves between the right heart and the hepatic veins determines a
passive congestion of the liver whenever there is any serious hindrance
to the passage of blood through the right heart and lungs. The tardy
circulation through the liver (5 mm. per second) also predisposes to
congestion. The great development of the circulatory system in the
liver, and its dilatability predisposes it to such congestions in a
pre-eminent degree. For the same reason the liver suffers in the horse
that is attacked with pulmonary congestion, whether as the result of
overwork or of heat congestion. It will also suffer from compression of
the lungs by false membranes or hydrothorax, or obstruction, by œdema,
hepatization or infarction. The toxic matters produced in infectious
diseases, and especially those affecting the intestinal canal and its
connections, are arrested in the liver and contribute to hyperæmia.