The antituberculosis vaccine of Calmette, known as B C G, consists of a strain of bovine tubercle bacilli, originally virulent, which, through long cultivation on bile-containing mediums, has lost its pathogenicity for animals and man. According to the original statement of Calmette,1advocated for a long time, this organism should be absolutely avirulent, and should lack the power to produce any specific tissue changes. Injected into, or ingested by, laboratory animals, the B C G should be absorbed and carried to the regional lymphatic glands, where it should enter into a sort of symbiosis with the cells, and call forth no demonstrable tissue reaction. Control experiments, first reported by Kraus2of Vienna, have shown, however, that the statement concerning the avirulence of the B C G was not quite true, being subject to some modification. A typical, but benign, spontaneously healing, tuberculosis does result from its inoculation into