THE Medical Research Council's War Memorandum, No. 11, entitled "The Control of Cross-Infection in Hospitals" (London: H.M. Stationery Office, 1944. 6d. net) epitomizes a great deal of research on this important question. Cross-infection, says Sir Wilson Jameson in his introduction, is most apparent and dangerous among infantile and juvenile patients in hospitals, so that this memorandum deals mainly with the risks in children's wards; but it is pointed out that the risks exist also among children at home and wherever else they assemble. Nor are adults by any means free from them. The risks are naturally greatest where infectious diseases are being treated, but they exist in every hospital ward; and, when a cross-infection occurs, the cost of it may be so high that any measures taken to prevent it are in the long run economical, even if these include, as they often must, building alterations.