The best defined group is that of the _granulomata_, which includes such important diseases as tuberculosis and syphilis, and in which different types of chronic inflammation are caused by infection with a specific organism, all having the common character, however, that abundant granulation tissue is formed in which cellular changes are more in evidence than changes in the blood vessels, and in which the subsequent degeneration and necrosis of the granulation tissue results in the breaking down and destruction of the tissue in which it is formed. Another group is that in which chronic inflammation is due to mild or attenuated forms of pyogenic infection affecting especially the lymph glands and the bone marrow. In the glands of the groin, for example, associated with various forms of irritation about the external genitals, different types of _chronic lymphadenitis_ are met with; they do not frankly suppurate as do the acute types, but are attended with a hyperplasia of the tissue elements which results in enlargement of the affected glands of a persistent, and sometimes of a relapsing character. Similar varieties of _osteomyelitis_ are met with that do not, like the acute forms, go on to suppuration or to death of bone, but result in thickening of the bone affected, both on the surface and in the interior, resulting in obliteration of the medullary canal. A third group of chronic inflammations are those that begin as an acute pyogenic inflammation, which, instead of resolving completely, persists in a chronic form. It does so apparently because there is some factor aiding the organisms and handicapping the tissues, such as the presence of a foreign body, a piece of glass or metal, or a piece of dead bone; in these circumstances the inflammation persists in a chronic form, attended with the formation of fibrous tissue, and, in the case of bone, with the formation of new bone in excess. It will be evident that in this group, chronic inflammation and repair are practically interchangeable terms. There are other groups of chronic inflammation, the origin of which continues to be the subject of controversy. Reference is here made to the chronic inflammations of the synovial membrane of joints, of tendon sheaths and of bursæ--_chronic synovitis_, _teno-synovitis_ and _bursitis_; of the fibrous tissues of joints--chronic forms of _arthritis_; of the blood vessels--chronic forms of _endarteritis_ and of _phlebitis_ and of the peripheral nerves--_neuritis_. Also in the breast and in the prostate, with the waning of sexual life there may occur a formation of fibrous tissue--chronic _interstitial mastitis_, _chronic prostatitis_, having analogies with the chronic interstitial inflammations of internal organs like the kidney--_chronic interstitial nephritis_; and in the breast and prostate, as in the kidney, the formation of fibrous tissue leads to changes in the secreting epithelium resulting in the formation of cysts.