Apparatus is disclosed for the safety monitoring of a dialyzer including at least one holder for holding a container for a powdered substance in which the holder includes a supply end for supplying a liquid to the container and a delivery end for delivering liquid containing the powdered substance from the container to a concentrate pump. An insulating region can contact the edges of each microelectronic element and at least portions of the traces of each microelectronic element extending beyond the respective first edges. A backward-traveling drive train is adapted to be driven by engaging one of the first and second clutches. The two descriptors are discriminated from one another in that the first descriptor address location is a location of an active descriptor and the second descriptor address location is a location of a reservelookahead descriptor. A subassembly is disposed over the compression mold, defining a center seat and including at least one cushion attachment support disposed adjacent to the at least one open section.