Abstract
Infected mice which were successfully treated with chemo-therapeutic agents are capable of withstanding homologous re-infection with Staphylocoecus aureus or Eschertchia coli within 24 hr. This explains why these infections respond excellently to a single Installment of treatment. In infections with Klebsiella and Pneumococci, [Diplococ-cus pneumoniae] resistance takes longer to build up, whereas resistance to Streptococci and Pasteurella falls to develop at all. In such infections, chemotherapy continued over a period of several days yields better results.