The character of the material discharged from an ulcer will vary according to the category in which it belongs. The healthy, healing, or granulating surface, often spoken of as ulcer, discharges a material in gross appearance much resembling pus from an acute abscess; in consistency, color, and other appearances it is the same. Nevertheless, its origin is essentially distinct. This material represents simply the waste of reparative material, sent up to the surface for the purpose of hurrying the process. Its fluid, like that of pus, comes from the serum of the blood; its corpuscular elements, like those of pus, are leukocytes or wandering tissue cells, which have been furnished in great numbers--in fact, in excess. As it comes to the surface--or as, rather, it is rejected from the surface, being superfluous in amount--it is likely to become contaminated with bacteria by contact infection, and consequently may be seen under the microscope to contain various microörganisms. This contamination, however, has been final, accidental, and irrelevant. This material is _not pus_; has no infectious properties, except those which may accidentally be conveyed to it; represents no warfare of cells, only excess of supply or overdemand; and should be spoken of as _pyoid_ or _puruloid_ material, and never confused with pus. In amount it will vary according to the activity of the reparative endeavor, and somewhat according to the amount of irritation of the surface by dressings which may be applied. If a granulating surface is absolutely protected from possibility of contact infection, it will never contain microörganisms; while this _pyoid_, if allowed to remain too long, especially when infection is permitted, may decompose and become irritating, and is a material to be gently dislodged by a spray or an irrigating stream with each dressing, which dressing should be made once in twenty-four to sixty hours. PROCESSES OF REPAIR.