Pass steam through the apparatus (6.1) for at least 15 min. With steam passing through the outer jacket of the apparatus(steam outlet open), introduce into the inner tube 10 cm of the acidified serum by pipette (6.4). If foaming is a difficulty, 1 drop of a suitable antifoaming agent may be added. Place a 100 cm3 graduated cylinder under the tip of the condenser to receive the distillate. Partially close the steam outlet to divert steam into the inner tube. Pass steam gently at first, then fully close the steam outlet and continue distilling at a rate of 3 cm /min to 5 cm3 /min until 100 cm of distillate has been collected.