Abstract: An observation cell arrangement for flow perfusion of a sample to be examined, the arrangement comprising a flow cell (21) having a cavity therein to receive the sample, the flow cell (21) arranged to receive a flow of fluid through the cavity that is directed over the sample from a cavity inlet (22) to a cavity outlet (23), the cavity inlet (22) associated with a fluid supply line, and a first flow supply path (24) connected to the fluid supply line via a valve (39), the first flow supply path (24) adapted to receive pressure from a pressure source comprising a pressure reservoir (29) to drive fluid flow through the cavity at a desired flow rate