A Simple Inexpensive Method for Concentrating Serum Under Sterile Conditions

Cellophane in sheets has been used for some time as a dializing membrane, and bags made of these sheets have been used as dializing bags.

Seamless tubes of cellophane, known commercially as sausage casings, also have been used for similar purposes.

Schwartzman¹ has made use of cellophane bags in the “preparation and preservation of immunologically active bacterial products.”

Kendall² has used cellophane tubes for concentrating antiserums and antibody solutions with the aid of a very interesting, simple negative pressure dialysis apparatus which he has devised. Undoubtedly others have used cellophane for similar purposes.

Apparently it is not well known that cellophane can be sterilized in an autoclave at 15 pounds pressure for 30 minutes without changing any of its important characteristics.

It is very simple to make up cellophane bags out of cellophane tubing—simply tied off with heavy twine at one end and with a one-hole rubber stopper tied in at the other end. Through the hole in the stopper a piece of glass tubing is inserted and its end covered with filter paper. The completed bag is sterilized in the autoclave. After it has cooled, sterile, filtered serum is introduced and the bag suspended in front of an electric fan in a room or in a mechanical refrigerator. It has been found that moisture will evaporate from a large cellophane tube filled with serum (about 1,000 cc.) in front of the fan at room temperature at the rate of 20-25 cc. an hour, and almost this fast in the refrigerator. In small amounts, 1-20 cc, in small bags, the serum will concentrate or dry even more quickly.

The serum can be concentrated to any desired degree or can be completely dried. Since the cellophane is impervious to bacteria the serum will remain sterile. When the desired concentration has been reached the serum either can be used or put into sterile bottles and kept.