An apparatus for receiving fluids and for precise extraction of individual phases of the received fluid, which comprises a cylinder in which a plunger is reversibly movable back and forth along the longitudinal axis of the cylinder, wherein the plunger bottom (11, 65) - when viewed from above - has in its middle area a hole-like cut-out, which is indirectly or directly connected in a fluid-tight manner or capable of being indirectly or directly connected in a fluid-tight manner - through the plunger - to a completely or partially transparent tube extending on the rod side and aligned along the longitudinal axis of the cylinder, wherein the inner diameter of the lumen of the tube is in the range of 0.5 mm to 10.0 mm, the length of the tube and of the lumen thereof is in the range of 5.0 cm to 15.0 cm, and wherein a reversibly closeable end cap is provided on the free end of the tube projecting vertically upwards (with the cylinder aligned vertically), wherein a screw thread-like and/or conical coupler device for a syringe is provided in the end cap and wherein a protrusion of the end cap extending horizontally outwards beyond the outside of the tube serves as a finger support during the aspiratory movement of the plunger and is in the range of 5.0 mm to 40 mm and wherein in the zone of the center of the bottom of the cylinder, provision is made of a screw thread-like and/or conical coupler device on the outside for a canula or for a screw-on or push-on pedestal and wherein in the upper region of the free end of the cylinder opposite the bottom, outer circumferential or opposing projections are provided for finger support, characterized in that the end cap comprises a container with a U-shaped cross section or with a cross section corresponding to a letter C tilted by 90° to the side, wherein a lid for the indirect or direct closure of the upper opening of the container and for the indirect or direct closure of the cone - provided in the container - of a coupler device for sealingly accommodating the tip of a syringe is indirectly or directly reversibly hinge-connected to an area of the free edge of this container by means of a hinge and wherein in the lower bottom zone of the container, provision is made of a vertically upwardly aligned coupler device for a syringe, which has a cone for centering and locking the tip of a syringe and a male thread for the engagement of a female thread which annularly surrounds the tip and which is arranged on an annular projection, wherein the container and the coupler device for a syringe are formed integrally with each other or are reversibly or permanently interconnectable by means of a thread, a latch connection, a snap-in connection, a plug-in connection, a rotary connection or a bayonet connection, wherein the coupler device for a syringe is connected downstream and in a vertically downwardly aligned direction indirectly or directly to a coupler device for the free, upper end of the tube, wherein a one-piece or multi-piece device for indirect or direct fluid-tight closure of the cone of the coupler device is provided on the inside of the lid and wherein a device is provided on the inside of the lid for a lid-centering engagement between the male thread of the coupler device and the inner wall of the container when the lid is closed.