Blood samples were collected after informed consent from 11 normal adult controls aged 24 to 36 years who had not ingested any medication for 10 days before evaluation, and from 11 normal full-term neonates. All infants weighed more than 2,500 g and were born of healthy mothers after full-term pregnancies and uneventful deliveries. Immediately after delivery, clamps were placed on the umbilical cord, a 19-gauge needle was inserted into the umbilical vein, and blood was drawn into a plastic syringe. Blood samples were also obtained on 8 infants aged 3 to 5 months.

Blood samples were mixed with 0.126 M trisodium citrate. The adult blood was anticoagulated by using 9 parts of blood to 1 part citrate. To adjust for the higher hematocrit of cord blood, the blood-citrate ratio in the latter experiments was 11: 1. Platelet-free plasma was obtained by centrifugation of the citrated blood for 15 minutes at 1,800 x g.