Around the margin of the site of an acute abscess a barrier is formed by condensation and cell infiltration of the surrounding tissues. This is not a distinct wall nor membrane, yet, nevertheless, serves as a sanitary cordon to confine the mimic conflict within reasonable bounds. This is the zone of real inflammation; within it there are tissue destruction and coagulation necrosis. By virtue of the peptonizing power of the pyogenic organisms the parts involved in this necrosis gradually liquefy the intercellular substance dissolving first. It is this which in the main forms the fluid portion of the pus. Various tissues show widely differing resistance to this softening process. In true glands the interlobular septa seem to break down first, and in this way suppuration extends around the acini or gland lobules, and thus pus may contain masses of easily recognizable size. These masses are ordinarily known as _sloughs_. It is by virtue of the so-called lymphoid cells, which are those principally involved in producing the barrier or boundary of the acute abscess as above described, that granulation tissue is formed, which takes up the effort of repair as soon as pus is evacuated. This boundary has no sharp limit, but shades off into healthy surrounding tissues. Under the term “abscess” is meant that which is described as _acute abscess_. Under certain circumstances, especially when they are produced by the facultative pyogenic organisms rather than the obligate, abscesses form more slowly, and may be spoken of as _subacute_. These are terms used in contradistinction to the so-called _cold abscesses_, which, although clinically bearing a certain resemblance to the acute, are in almost every pathological respect different from it. Cold abscesses will be considered under the head of Tuberculosis. It is possible to have an acute pyogenic infection of a cold abscess; in such case we have acute manifestations. _Gravitation abscesses_ are those where pus forming in one part tends to migrate, usually in the direction in which gravity would take it, extending into portions deeper or lower. Perhaps the best illustration of this is the pointing of a psoas abscess below Poupart’s ligament. _Metastatic abscesses_ are those which are formed as the result of embolic processes, each one being in miniature a repetition of a lesion which has occurred at some other part of the body. The underlying fact concerning metastatic abscesses is that the primary process has occurred in some other portion of the body, whence it has been distributed as above. These will be considered in the chapter treating of Pyemia.