Lymphangitis: The red streaking and gland (lymph node) swelling in the area of an injury especially on the extremities. It is usually caused by a bacterial infection with Streptococcus. The bacteria enter the body through a cut, scrape, bite or wound of some sort. The bacteria can get into the lymphatic system, which is part of our immune system. The bacterial infection spreads rapidly in the lymph channels (causing the red streaking) and lymph nodes (causing hard swollen "knots" under the skin). If left untreated, the bacteria can spread in the skin around the area, causing cellulitis, and also rapidly spread to the bloodstream, causing sepsis. In the days before antibiotics people referred to lymphangitis as "blood poisoning" due to the infection rapidly causing severe illness and sometimes death.