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580 Influence of age and length of residence.— Liver abscess may occur at any age after childhood, but is most common between 20 and 40. It is most prone to show itself during the earlier years of residence in the tropics (40 per cent, in the first three years), although the older resident is by no means exempt.

Influence of malaria.— Malaria, by causing frequent attacks of hepatic congestion and by lowering the general vitality, may have some predisposing influence; but, as already pointed out, malarial hepatitis is essentially of a plastic and not of a suppurative nature. It is a common mistake to suppose that malaria causes the suppurative liver disease of the tropics; the two concur geographically to a certain extent, but are in no way etiologically identical.

Morbid anatomy.— It may be inferred from the symptoms that in the early stages of suppurative hepatitis there is general congestion and enlargement of the liver; in some instances this condition may be more or less confined to one lobe or even part of a lobe. Later, as we know more especially from observations in cases that have died from the attendant dysentery, one or more greyish, ill-defined, anæmic, circular patches, ½-1 in. or there-abouts in diameter, in which the lobular structure of the gland cannot be made out, are formed. These grey spots are very evident on section of the organ. A drop or two of a reddish, gummy pus may be expressed from the necrotic patches— for such they are. Still later, the centres of the patches liquefy, and distinct but ragged abscess cavities are formed. An abscess thus commenced extends partly by molecular breaking down; partly by more massive necrosis of portions of its wall; partly by the formation of additional foci of softening in the neighbourhood and subsequent breaking down of the intervening septa. The walls of such an abscess have a ragged and rotten appearance. Spherical on the whole, there may be one or more diverticula extending from the main cavity; or contiguous abscesses may break into each other and communicate by a sinus. Occasionally a thickened blood-vessel is met with, stretching across