Abstract: Plasma is separated from a blood product such as SAG-M or anticoagulated whole blood by flowing the blood product across a membrane. The membrane has a voids volume of greater than 50%, a pore size of less then 0.65 .mu.m and a plasma flow rate of greater than 0.04 ml/min.cm.sup.2 with a specified value of blood product and with a specified transmembrane pressure. The surface of the membrane contacted by the blood product has a smoothness of less than 0.5 .mu.m.

Abstract: A communications network, having an SDH transmission line with four main channels, is provided, at four different tributary connection nodes, with respective add/drop multiplexer units for permitting interchange of information signals between the main channels and tributary channels of the network connected to respective tributary ports. Each add/drop multiplexer unit includes a time slot interchange unit through which a pair of the main channels pass but which bypass the other two main channels. Because different pairs of the main channels pass through the different time slot interchange units, signal interchange is possible between any one of the main channels and any one of the tributary channels, even though the time slot interchange unit at each node need not have an interchange capability sufficient to enable signal interchange between each tributary channel at the node concerned and any one of the main channels. The add/drop multiplexer units can be located together at a single node, if required.