Cellulitis is an acute affection resulting from the introduction of some organism--commonly the _streptococcus pyogenes_--into the cellular connective tissue of the integument, intermuscular septa, tendon sheaths, or other structures. Infection always takes place through a breach of the surface, although this may be superficial and insignificant, such as a pin-prick, a scratch, or a crack under a nail, and the wound may have been healed for some time before the inflammation becomes manifest. The cellulitis, also, may develop at some distance from the seat of inoculation, the organisms having travelled by the lymphatics. The virulence of the organisms, the loose, open nature of the tissues in which they develop, and the free lymphatic circulation by means of which they are spread, account for the diffuse nature of the process. Sometimes numbers of cocci are carried for a considerable distance from the primary area before they are arrested in the lymphatics, and thus several patches of inflammation may appear with healthy areas between. The pus infiltrates the meshes of the cellular tissue, there is sloughing of considerable portions of tissue of low vitality, such as fat, fascia, or tendon, and if the process continues for some time several collections of pus may form. _Clinical Features._--The reaction in cases of diffuse cellulitis is severe, and is usually ushered in by a distinct chill or even a rigor, while the temperature rises to 103°, 104°, or 105° F. The pulse is proportionately increased in frequency, and is small, feeble, and often irregular. The face is flushed, the tongue dry and brown, and the patient may become delirious, especially during the night. Leucocytosis is present in cases of moderate severity; but in severe cases the virulence of the toxins prevents reaction taking place, and leucocytosis is absent. The local manifestations vary with the relation of the seat of the inflammation to the surface. When the superficial cellular tissue is involved, the skin assumes a dark bluish-red colour, is swollen, œdematous, and the seat of burning pain. To the touch it is firm, hot, and tender. When the primary focus is in the deeper tissues, the constitutional disturbance is aggravated, while the local signs are delayed, and only become prominent when pus forms and approaches the surface. It is not uncommon for blebs containing dark serous fluid to form on the skin. The infection frequently spreads along the line of the main lymph vessels of the part (_septic lymphangitis_) and may reach the lymph glands (_septic lymphadenitis_).