Wounds of the fourth class, although the most highly characteristic of the form of accident, were in many instances the most favourable in regard to their course. The tracks might course directly across the joint in any direction, or they might course obliquely, traversing either one or both the component bones. In the latter case the exit might be in the diaphysis, and be accompanied by the separation of an exit fragment such as is illustrated in fig. 52, p. 169. The particularly favourable character of the direct transverse and antero-posterior wounds depended on the slight amount of splintering of the bones, the limited nature of the opening into the joint, and the shortness of the tracks in the soft parts, which ensured that, even if infection did occur, the resulting pus was near the surface, and generally spread in that direction and escaped. Wounds of the fifth class were the most dangerous, but the danger was entirely a secondary one, dependent on the occurrence of infection. These injuries were liable to be accompanied by the presence of extensive irregular wounds of the soft parts, in which suppuration was frequent, and the suppuration of the joint frequently meant subsequent amputation, if not a worse result. _Course and symptoms of wounds of the joints._--The immediate result of any perforation of a joint was the development of intra-articular effusion. This consisted of synovial fluid admixed with a varying proportion of blood. The degree of synovitis was apt to vary with the amount of force expended in the production of the injury; for this reason both high velocity and irregular impact were of importance in this relation. The constant feature, however, depended on the effusion of blood; this was not rapid, or, as a rule, very abundant, but tended to increase during the first twenty-four hours. It resulted in a swelling of the joint, which possessed some peculiar features. At first elastic and resilient, it slowly decreased in volume with the assumption of a soft doughy character on palpation. In the case of the knee, where readily palpated, it very much resembled a tubercular synovial membrane, except for its extreme regularity of surface; still more closely the condition noted in a haemophilic knee of some duration. Absorption took place with some rapidity, and except for slight thickening, the joints might appear almost normal, in a period of from two to four weeks. With the development of the effusion there was local rise in temperature of the surface, and in a considerable number of the cases a general rise of temperature.