Dead tubercle bacilli, when injected into a guinea-pig or other animal, are capable of producing either local or general effects, depending chiefly on the number introduced. As to whether the ingestion of dead tubercle bacilli is harmful or beneficial, or without effect, the evidence is not clear, as there has been but little experimental work done on this subject. In Germany and other European countries meat of tuberculous animals is not destroyed, as is required by the federal regulations of this country. Such meat in certain European countries is cooked under official surveillance and sold at a lower price. This is the so-called Freibank system. The question assumes great practical importance on account of the use of pasteurized milk, cooked meat from tuberculous animals, and other food products containing dead tubercle bacilli. It is of the utmost importance to determine if the susceptibility to tuberculosis is increased, decreased, or not altered by the previous eating of food containing tubercle bacilli killed by heat. The experiments which we wish to report were designed to simulate as closely as possible the effect produced by the ingestion of pasteurized milk or milk products. The tubercle bacilli were heated at 600 C. for 30 minutes, mixed with butter, and fed to guinea-pigs daily (excepting Sundays) for 60 days. A low degree of heat was used to prevent altering the bacilli as much as possible and closely to simulate pasteurization. The animals were always given the dead bacilli mixed in the butter before receiving their usual morning feed. Control inoculations of the