1. The causative agent of infectious laryngotracheitis of chickens was found to be present in bacteriologically sterile tracheal exudate, spleens, and livers of diseased fowls.
2. The causative agent was present regularly in the tracheal exudate, in the spleens of about 60 per cent, and in the livers of about 30 per cent of chickens with active laryngotracheitis infection.
3. Suspensions of the spleen and liver were less effective in inducing the disease than those made from the tracheal exudate. This finding, together with the absence of pathological changes in the spleens and livers would seem to indicate that they are not actively involved but that the causative agent is carried to them by way of the blood.
4. The disease could, in our experience, be produced only in chickens Domesticated ducks and several wild and free-flying species of birds, including sparrows, crows, starlings, doves, and pigeons were found to be refractory, and so too were rabbits, guinea pigs, white rats, and one pig that was tested.