Three types of an uncomplicated fowl coryza, differing in the onset and duration of symptoms, developed after the intranasal injection into normal birds of exudate from natural cases. Protection tests were carried out with 2 of the types in an attempt to explain why the "bacillary" disease regularly ran a shorter course than the "exudate" disease. Reciprocal protection was demonstrated in one case, but in the other the birds which had recovered from the "bacillary" disease were susceptible to reinfection with exudate. There was no indication, however, that a second infectious agent was present in the exudate, and the failure to cross-immunize was ascribed, rather, to a reduction in the immunizing properties of the specific bacillus induced by artificial cultivation.
It was also noted that the coryzas produced by exudate and bacilli, respectively, could be transmitted from infected birds to normal ones by direct contact. In both cases 1 bird out of 5 failed to contract coryza on exposure. These 2 birds were later injected with the respective agents to which they had been exposed and found to be resistant.