The recognition of the characteristic elements, with or without caseation, is usually sufficient evidence of the tuberculous nature of any portion of tissue examined for diagnostic purposes.  The recognition of the bacillus itself by appropriate methods of staining makes the diagnosis a certainty; but as it is by no means easy to identify the organism in many forms of surgical tuberculosis, it may be necessary to have recourse to experimental inoculation of susceptible animals such as guinea-pigs.

The changes subsequent to the formation of tuberculous granulation tissue are liable to many variations.  It must always be borne in mind that although the bacilli have effected a lodgment and have inaugurated disease, the relation between them and the tissues remains one of mutual antagonism; which of them is to gain and keep the upper hand in the conflict depends on their relative powers of resistance.

If the tissues prevail, there ensues a process of repair.  In the immediate vicinity of the area of infection young connective tissue, and later, fibrous tissue, is formed.  This may replace the tuberculous tissue and bring about repair—­a fibrous cicatrix remaining to mark the scene of the previous contest.  Scars of this nature are frequently discovered at the apex of the lung after death in persons who have at one time suffered from pulmonary phthisis.  Under other circumstances, the tuberculous tissue that has undergone caseation, or even calcification, is only encapsulated by the new fibrous tissue, like a foreign body.  Although this may be regarded as a victory for the tissues, the cure, if such it may be called, is not necessarily a permanent one, for at any subsequent period, if the part affected is disturbed by injury or through some other influence, the encapsulated tubercle may again become active and get the upper hand of the tissues, and there results a relapse or recrudescence of the disease.  This tendency to relapse after apparent cure is a notable feature of tuberculous disease as it is met with in the spine, or in the hip-joint, and it necessitates a prolonged course of treatment to give the best chance of a lasting cure.

If, however, at the inauguration of the tuberculous disease the bacilli prevail, the infection tends to spread into the tissues surrounding those originally infected, and more and more tuberculous granulation tissue is formed.  Finally the tuberculous tissue breaks down and liquefies, resulting in the formation of a cold abscess.  In their struggle with the tissues, tubercle bacilli receive considerable support and assistance from any pyogenic organisms that may be present.  A tuberculous infection may exhibit its aggressive qualities in a more serious manner by sending off detachments of bacilli, which are carried by the lymphatics to the nearest glands, or by the blood-stream to more distant, and it may be to all, parts of the body.  When the infection is thus generalised, the condition is called general tuberculosis.  Considering the extraordinary frequency of localised forms of surgical tuberculosis, general dissemination of the disease is rare.