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The changes that ensue resemble in character those in other tissues, and the extent of the destruction varies according to the way in which the tubercle bacillus and the marrow interact upon one another. The granulation tissue may undergo caseation and liquefaction, or may become encapsulated by fibrous tissue "encysted tubercle."
The abscess tends to increase in size by progressive liquefaction of the inner layers, caseation of the outer layers, and the further invasion of the surrounding tissues by tubercle bacilli. In this way a tuberculous abscess is capable of indefinite extension and increase in size until it reaches a free surface and ruptures externally.
From the addition of a sufficient number of leucocytes, the contents may resemble the pus of an ordinary abscess. The wall of the abscess is lined with tuberculous granulation tissue, the inner layers of which are undergoing caseation and disintegration, and present a shreddy appearance; the outer layers consist of tuberculous tissue which has not yet undergone caseation.
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.
The gumma does harm by displacing and replacing the normal tissue elements of the part affected, and by involving these in the degenerative changes, of the nature of caseation and necrosis, which produce the destructive lesions of the skin, mucous membranes, and internal organs.
It is to be understood, however, that operative treatment must always be preceded by and combined with other therapeutic measures. The caseation of tuberculous granulation tissue and its liquefaction is a slow and insidious process, and is unattended with the classical signs of inflammation hence the terms "cold" and "chronic" applied to the tuberculous abscess.
#Changes in the Tissues following upon the successful Lodgment of Tubercle Bacilli.# The action of the bacilli on the tissues results in the formation of granulation tissue comprising characteristic tissue elements and with a marked tendency to undergo caseation.
Tuberculous disease in muscle, while usually due to extension from adjacent tissues, is sometimes the result of a primary infection through the blood-stream. Tuberculous nodules are found disseminated throughout the muscle; the surrounding tissues are indurated, and central caseation may take place and lead to abscess formation and sinuses.
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.
If this fails, the distended sheath is laid open, the contents removed, the wall scraped, and the wound closed. A less common form of tuberculous disease is that in which the sheath becomes the seat of a diffuse tuberculous thickening, not unlike the white swelling met with in joints, and with a similar tendency to caseation.
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