The contents of the cold abscess are, in some instances at least, of acute origin, and consequently may have been originally pus or its near ally. On the other hand, in cases which have occurred very slowly this material is not real pus, but is a semifluid debris having certain properties which remind one of pus. It has been my effort hitherto to devise for this material a name which should distinguish it from pus and indicate what it really is. Inasmuch as most of it has been of a puruloid character, at least at one time, I have suggested that it be called _archepyon_ (_i. e._, originally pus or puruloid). As this flows from such a cold abscess, it is more or less watery and contains caseous, sometimes calcareous, nodules in masses of considerable size, and not infrequently sloughs of tissue and old shreds of white fibrous tissue which resist decomposition for a long time. This material has been thus imprisoned, sometimes for months or even years, and consequently has lost most of its resemblance to what it was originally. The organisms which first produced it have long since died, and it is practically sterile. If any organisms survive, they are the tubercle bacilli, which are more resistant and tenacious of life than the ordinary pyogenic organisms. This is why most culture experiments fail, and why even inoculation with the contents of an old cold abscess is often without effect even on most susceptible animals. _Nevertheless the bacilli which the semifluid contents do not contain may yet linger in the meshes of the pyophylactic membrane; and here lurks the greatest danger in dealing with these lesions._ In old cases the pyophylactic membrane is very tough and very adherent by its outer surface. It can sometimes be peeled off in strips of considerable extent, at other times cannot even be separated, or sometimes is so placed as to render it impossible to follow it to its termination. There must be _complete extirpation of this membrane_, or at least destruction; and when its removal is impracticable, failure to remove it should be atoned for by some powerful caustic, such as zinc chloride, nitric acid, caustic pyrozone or the actual cautery, which should be made to follow it to its ultimate ramification. The membrane and the tissues underlying, when thus cauterized, will separate as sloughs, and these will be replaced by presumably healthy granulations, which should be encouraged until the original cavity is filled or the surface healed.