Evaluation of difficulties in the standardization of human and bovine tuberculins

The tuberculins are made of mixtures of antigens. Certain elements are common to all tuberculins, others are particular to each one. Bovine and human tuberculins are widely different. This is the reason why the activities of a bovine tuberculin using a human tuberculin standard will be in a ratio of 1 to 5 according to whether the guinea-pigs were sensitized with human or bovine mycobacteria. Also, the activities measured for a given tuberculin might be different if the mycobacteria used in sensitization were inactivated or not, depending on the amount of Antigen L in the tuberculin or in the standard. Because BCG is well defined and used worldwide we propose that a new standard be prepared from BCG cultures, and that the animals be sensitized by live BCG. Two new units are proposed: Bovine Clinical Unit (B.C.U.) and Human Clinical Unit (H.C.U.).