Personal Investigation

One of the difficulties in determining the actual effectivity of BCG, especially in children where age at the time of exposure plays such an important part, consists in finding a homologous control material. Levine, V q e l and Rosenberg (1 938) emphasize this point particularly, and mention a number of factors which should be equal within the 2 groups to be compared. Most important is the intensity of the exposure (the bacillary frequency, massivity and also virulence) and the exposure age. It is well known that a tuberculosis exposure during the first year of life gives a much poorer prognosis than later. Further: milieu factors with differing social standards of living. An important factor here is the cooperation and intelligence of the parents, and the consequent significance of prophylactic memures. This factor is clearly illustrated in H . v. den Berg's (1929) publications. In children under 3 months, where the infection-bearing environment was prohylactically instructed, the mortality was 3.8 %, while the mortality in children in similar families which had no prophylactic instruction went up to