Abstract
Summary
PCA reactions are seldom elicited in conventional adult chickens in contrast to the positive reaction that are readily obtained in young and specific pathogen free (SPF) chickens. Adult germfree chickens also gave postive PCA reactions. Blood exchange experiments were performed among conventional adult chickens, young and SPF chickens. Conventional adult chickens became PCA positive after receiving blood from young or SPF chickens. This suggests that a factor exists in the blood of young and SPF chickens that facilitates the PCA reaction.
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