Haemolytic Complement Activity of Sera of Foetal and New-Born Lambs.

Determination of the haemolytic complement titres of serum from 24 foetal lambs bled at 77 to 149 days gestation failed to reveal this activity earlier than 123 days. Titres near the end of the gestation period of 150 days were still very low. Among serum specimens collected from 17 newborn lambs before suckling, three were still without demonstrable complement activity. During the first week titres rose considerably in all of these lambs, were higher at three weeks but at ten weeks were still below the adult level.A number of foeti had been injected with antigen mixtures at 50 to 111 days' gestation and had responded with antibody development to one or more of these antigens. The rate of development of complement in these treated foetal lambs appeared similar to that in their untreated twin controls.