From advanced gestation the differentiation is found in the general diffusion of the swelling and fluctuation, which is not confined as in gestation to the mobile uterine horns, with a series of enlargements each containing a solid nodular fœtus.
From hydrometra and pyometra there are the same pathognomonic differential features of the general diffusion of the swelling among the intestines, and its accumulation in one fluctuating mass at the most dependent part of the abdomen.
Tympany of the bowels causes uniform drumlike resonance, and the swelling does not sag and fluctuate in the lower part of the abdomen.
Abdominal obesity in old dogs gives the rounded swollen abdomen, but there is an entire absence of the pendulous and fluctuating features, and when punctured with the hypodermic needle it furnishes no fluid.
From tuberculosis it is distinguished by the absence of nasal discharge, or of tubercle bacilli in such discharge, or in the ascitic fluid, and the latter inoculated on guinea pigs or rabbits does not cause tuberculosis. The tuberculin test may also be resorted to.
Lesions. The liquid exudate has been found to amount to 30 or 40 quarts in large dogs (Hordt). It is often clear and translucent, of amber tint, though in some cases it is slightly opaque, or reddish yellow. It may remain fluid after extraction or again it may form a loose jelly. It may be red in case of soft tumors or other neoplasms. The liquid is very watery but may contain a considerable amount of fatty globules or granules, and a few epithelial cells and leucocytes. The peritoneum is pale or in advanced cases dull white from fatty degeneration of the epithelium.
Treatment. The first consideration is the removal of the cause. If this is a mere vicious action of the peritoneum, or the presence of a thrombus, or of operable tumor, or even of curable disease of the liver or kidneys, success may be hoped for, while in dilatation of the heart, insufficiency of the cardiac valves, irremediable disease of the lungs, liver or kidney, or malignant or inoperable tumor no such result can be hoped for.
Apart from the removal of the cause the first indication is to evacuate the liquid and this may be done with a large hypodermic needle or small cannula and trochar inserted by preference on or near the linea alba while the animal is in a standing position. Skin and instrument should be rendered thoroughly aseptic, and a bandage should be wrapped round the abdomen and gradually tightened as the liquid escapes. This to a large extent obviates the tendency to faint, or to cerebral anæmia which has caused sudden death in a number of cases. It also to some extent counteracts the sudden effusion of blood in the abdomen, which is at times determined by the sense of vacuity.
Injection of a solution of iodine (tincture of iodine 1 pt., iodide of potassium 1 pt., boiled water 20 pts.) has been employed sometimes with success, but in other cases it has roused a fatal inflammation. It is best adapted to a simple morbid, relaxed state of the peritoneum.
Saline purgatives (sulphate of soda or magnesia) are especially useful in constipated cases and should be pushed in continuous action, as far as the strength of the animal will warrant. By depletion from the portal system they oppose the tendency to mechanical transudation, while by rendering the portal blood more dense they strongly solicit endosmosis from the adjacent peritoneum.