The dissemination of tubercle bacilli has been examined in guinea pigs infected experimentally with human-type bacilli- from tuberculosis organs or with a culture of bovine type tubercle bacilli. The heavier the inoculum, the more rapid was the rate of spread of the bacilli in the body. Tubercle bacilli were discovered in the majority of the organs 1 hr. after subcut. inoculation. The brain appeared to be the last organ invaded. Examinations of the blood revealed that tubercle bacilli were present in the first few hrs. after inoculation and thereafter only at irregular intervals. Tne earliest microscopic changes appeared in the lymph nodes and the spleen at 24 hrs., and in the liver at 48 hrs., after infection.