In other words, the majority of cases of tuberculous pyarthrosis are due to primary bone disease. As the result of the tuberculous infection the bones become distorted, which is best illustrated in Pott’s disease of the spine; while, as the result of the constant irritation, joint ends become displaced by chronic muscle spasm, and joint contours entirely altered by expansion of the affected bone and thickening and infiltration of the overlying soft parts. I have often, for the sake of illustration to medical students, drawn a certain analogy (following Savory) of the gross resemblances between lungs and bones in their behavior when involved in tuberculous disease. In either case the structure is in a measure spongy and contains cavities and networks of tissue; in each case the structures are invested by a resisting membrane--in the one instance pleura, in the other periosteum. Again, each is closely related to a serous cavity--the lungs to the pleural cavity, the bones to the serous cavities of the joints. Tuberculous disease manifests a predilection for the extremities of both organs. Perforation into the adjoining serous cavity is frequent, and previous to perforation collections of serous fluid are frequently noted--in one instance pleurisy, in the other hydrarthrosis. Moreover, these fluids may frequently become contaminated, and then become purulent, constituting empyema or pyarthrosis as the condition may be. One sees, too, in each place the same striking combinations of weakening of tissue and strengthening in order to atone for the undermining of the disease. These are not all of the similarities that might be adduced, but are perhaps sufficient for the purpose of showing that tuberculous disease is essentially one and the same thing, no matter what tissue is invaded. _In the tendon sheaths and bursæ_ we frequently find manifestations of tuberculosis. When seen early these are always in the direction either of miliary affection, or, most commonly, of tuberculous gumma, while when seen late the disease has usually advanced to the point of suppuration, and we now have cold abscess of the affected part.