Haemolysis in chicken serum. II. Ontogenetic development.

Development of total complement (C) and C1 activity was followed in Line 96 chickens from day 13 of embryonic life to 40 days post-hatching. Both activities were demonstrable on day 13, and levels rose slowly in the late prehatching period. At hatching, on day 21, there was a sharp rise in both activities; both titres were roughly five times those of day 19 embryos. Further increases were seen to about day 10, followed by a levelling off (perhaps even a drop in the case of C1) for about 10 days. On about the twenty-first day the titration curve rose again. The source of the C detected in the embryo and young chicken is unknown. The pattern is consistent with transfer from the egg, but it might also reflect synthesis by the developing animal.