Effect of bacterial contamination of the tumor on tumor-host relationships.

Host effects produced by the tumor were studied in rats with the Walker carcinoma 256 either contaminated with or free of Salmonella typhimurium. In the absence of bacterial infection, tumor growth caused slight changes in most of the systems studied. Usually the changes were most pronounced when the tumors were 10-15 per cent of the total body weight. In the presence of infection, the changes in liver catalase activity, phagocytosis by the reticuloendothelial system, plasma iron, liver weight, spleen weight, and adrenal weight were large and progressive with tumor growth. Increases in serum aldolase activity and fatty acid concentration in the tumor-bearing animals were not influenced by S. typhimurium infection. Thymus weight, hemoglobin con centration, and plasma proteins could be altered by infection in tumor-free rats. Simi lar alterations occurred in the tumor-bearing rat in both the presence and the absence