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584 Pathology.— The pathology of liver abscess has been a fruitful source of speculation and controversy. Much confusion has crept into the question from attempts to separate, etiologically and pathologically, multiple from single liver abscess. The former is often called " pyæmic abscess" or "dysenteric abscess," and has been set down as being the peculiar sequel of dysentery; the latter has been called and considered the " tropical abscess " par excellence, and regarded as idiopathic and entirely unconnected with dysentery.

As already pointed out, a careful examination of cases and statistics shows that both forms of abscess, single and multiple alike, are, in the vast majority of instances, clearly associated with dysentery. In their respective clinical histories, in their symptoms, in the characters of their walls and contents, in the frequent presence of amoebae, single and multiple abscesses are practically identical. The only difference between them is a numerical one— a circumstance quite inadequate to base a doctrine of specific distinction upon. The view which I incline to hold on this subject has already been partly given in the section on etiology. There are two factors which are principally concerned in the production of liver abscess: (1) the predisposing— weakening of the resistive faculty of the liver by chronic congestion or tissue degeneration, and, perhaps, other subtle changes brought about by a combination of climatic, dietetic, and other tropical conditions; (2) the exciting— some micro-organism, streptococcus, staphylococcus, Bacterium coli commune, or other parasite, but especially the amœba, which, coming from the ulcerated dysenteric colon, or by way of the portal circulation (Marshall has demonstrated amoebae in a thrombus in a branch of the portal vein), gains access to the liver and proliferates in the weakened tissues. In at least 90 per cent, of cases the micro-organism is associated with or derived from dysenteric processes in the colon. Whether the resulting abscess be single or multiple is more or less a matter of accident.