A hemodialysis machine including a cartridge which defines a fluid pathway for delivering a dialysate solution base to a mixing pump, a main body having a platen which, in use, abuts the cartridge, the cartridge having a chassis with a platen side covered by a deformable membrane which, in use, abuts the platen, the chassis and membrane defining the flow path, the flow path including a dialysate base solution pump chamber, the platen having a dialysate base solution pump cavity which, collectively with the dialysate base solution pump chamber, forms a dialysate base solution pump for pumping dialysate base solution to the mixing pump by actuation of the membrane, wherein the volume of the dialysate base solution pump cavity is variable so as to allow a variation in the volume of dialysate base solution pumped from the dialysate base solution pump chamber to the mixing pump chamber on each stroke of the solution pump.
