In order to obtain knowledge of the fate of tuberculin in the organism the substance was injected into normal animals. After injection, tuberculin rapidly disappears from the vascular system and does not reappear in the urine till after several hours. In the meantime the substance is bound in the organism, probably in the bones and in the liver. Living cellsin vitroalso have the faculty of binding tuberculin.Through numerous experiments a difference is demonstrated between the complements of different sera, a fact which strongly supports the theory of the plurality of complements. Evidence is brought forth which points to a difference between tuberculous and non-tuberculous complement.Tuberculin is highly noxious to the vitality of the white blood corpuscles, and more toxic to corpuscles from tuberculouos organisms than from not-tuberculous organisms. A certain protective power in regard to the toxic action of tuberculin is found in the serum. This power is greater in serum from normal organisms, than in serum from tuberculous organisms.By means of vital staning a difference is demonstrated between the effects of tuberculin upon the leycocytes from normal and tuberculous animals.