A. Our Germ Tube Cryo™ (Cat. no. Z217) consists of newborn calf serum and Tryptic Soy Broth. It comes pre-measured and ready-to-use in small CryoSaver™ vials that are stored in the freezer. This eliminates the hazards of using human serum and saves the technologist time, since it is "ready-to-use.