Evidence is presented that the growth capacity of chick embryo tissue for the fowl coryza bodies is conditioned by a diffusible cellular component which is essential for their multiplication. This growth factor is inactivated at pH 6, but withstands a temperature of 100°C. for 60 minutes. An amount sufficient to promote a normal growth of the specific bodies may be present in tissue culture supernatants long after its content in the tissue is exhausted.
Postembryonic tissue (liver and spleen) contains a variable amount of growth factor and is not a satisfactory substitute for the chick embryo. Multiplication of recently isolated fowl coryza bodies is not demonstrable in nutrient media enriched with blood. Experiments with one strain, however, indicate that an adaptation to fluid blood in an agar medium may take place after many generations in tissue culture.
The probable bacterial nature of the fowl coryza bodies is discussed on the basis of their cultural requirements.
