Abstract
There are a number of conditions in which use of antibiotics for protection against bacterial invasion is not justified, either because this type of complication is very uncommon or because there is proof that the desired result will not be produced. It is striking that the clinical areas in which prophylaxis was applied most widely are those in which its use was based mainly on clinical impression rather than on fact derived from careful study. It is in some of these situations that more investigation is necessary before the true value of the chemoprophylactic procedures which were employed can be determined.