Abstract: The present invention includes a method and apparatus for transferring a specific amount of solid, gaseous or fluid medium to or from a space through the wall of a flexible, membranous member which encloses the space. A suction force is applied on part of the membranous member resulting in a locally increasing yet allowable deformation by tensioning of the membranous member. The pretensioned membranous member is then perforated by a needle-shaped instrument. This vacuum fixation is obtained by using a cup-shaped member of which a circumferential edge is first brought into a sealing contact with the membranous member before the suction force is applied. A hollow guiding tube guides a catheter-needle unit. One end of the hollow guiding tube is provided with the cup-shaped member which is connected to the vacuum outlet, preferably a disconnectable vacuum outlet.