Abstract: A method for treating blood uses a tubular body fluid passageway member at least part of which is made of a flexible material, an outer tubular member which is made of a nonflexible material and contains said tubular body fluid passageway member hermetically enclosed therein, a pressure detecting member for monitoring the pressure of the flowing body fluid by means of a fluid filled in the hermetically closed space between the outside surface of said tubular body fluid passageway member and said outer tubular member without substantial contact of the body fluid with air, and a body fluid filtering member comprising a filter. The method is especially useful for non-anticoagulant hemodialysis.

Abstract: Semi-permeable membranes of regenerated cellulose are subjected to wet-heat sterilization at a temperature of 105.degree. to 140.degree. C. During the treatment, the membranes are maintained in contact with an aqueous medium such as water or physiological saline. For the dialysis of body fluids, hollow fiber, semi-permeable membranes so sterilized exhibit a sonic modulus of at least 6.5.times.10.sup.10 dynes/cm.sup.2. Hollow fibers made of cuprammonium regenerated cellulose are particularly preferred for the above purpose.