One inevitable law seems to govern collections of pus, that when they _advance_ or migrate in any direction it is in that of _least resistance_. This causes them to take peculiar and sometimes disastrous courses, but it is a law which is never violated. It leads to the bursting of abscesses into the brain, into the pleural cavity, into the peritoneal cavity, the bowel, and elsewhere; it leads to a condition where pus may travel along a path even a foot or more in length, rather than come to the surface, a distance of perhaps an inch, and affords one of the best reasons for early operative interference so that the disastrous effects of burrowing may be obviated. When the pus is limited to a drop or fraction thereof the abscess is called a _furuncle_, especially when in the skin. The average “boil” of the layman is a subcutaneous or subfascial abscess. When the infiltration is pronounced, and when there has been more or less extensive destruction of tissue, with perhaps formation of numerous outlets for the escape of pus and detritus, it is known as a _carbuncle_. (See Chapter XXVI.) In certain conditions small superficial furuncles or boils form, sometimes in great number and almost synchronously, or, as it were, in crops. This condition is known as _general furunculosis_. =Signs and Symptoms of Abscesses.=--The appearances by which pus may be suspected or detected are those of congestion and hyperemia, more or less abruptly circumscribed and markedly accentuated. Along with these there is more or less edema or edematous infiltration of the skin and overlying tissue, which permits of that peculiar appearance known as “pitting on pressure.” Often, too, there is a distinctly edematous swelling of the parts, especially around the margin, with brawny infiltration of the centre of the infected area. Numerous vesicles occasionally are noted upon the skin, which may be filled with reddish serum. When softening and pus formation occur, there is a condition which to the palpating fingers gives the characteristic sensation known as _fluctuation_. Fluctuation simply points out the presence of fluid beneath; but when in an area marked as thus described fluctuation is noted, it means the presence of pus. It is detected by manipulating in a direction parallel to and concentric with the axis of the limb or part. The pain is also in most instances significant; patients speak of it as having an intense and throbbing character. With these local signs occur symptoms indicating some degree of septic intoxication, _i. e._, pyrexia, chills, malaise, sweats, etc., which are corroborative indications, their intensity being a reasonably correct index of the severity and gravity of the local infection. When a deep-seated abscess is suspected a careful blood count will often permit a diagnosis to be made. This is conspicuously true of cases of appendicitis. If leukocytosis is established there should be immediate operation. (See Chapter II.)