in the rear wall 13 c of the spring clip 13 so that the spring clip 13 is removed from the catheter hub with the needle 9 while simultaneously the spring arms 13 a and 13 b of the spring clip cover the needle tip completely protecting and blocking it in this separated position shown in fig2 the valve disc 7 due to its elasticity closes the through hole for the hollow needle 9 so that no blood can flow out through the catheter 4 as fig6 shows the valve disc is provided for example with three slits 7 a starting from the middle and extending radially over a short section x forming elastic flaps 7 b therebetween which can be expanded by the hollow needle fig3 shows the insertion of a syringe 14 in the catheter hub 2 wherein the neck portion 14 a of the syringe comes to abut on the plunger section 10 b of the valve actuating element 10 and presses it against the valve disc 7 so that the truncated cone shaped locating section 10 a outwardly displaces the flaps 7 b of the valve disc and thereby opens the valve so that a liquid can be inserted from the syringe 14 into the catheter 4 the incline of the truncated cone on the locating section 10 a and the displacement path of the actuating element 10 relative to the valve disc 7 are designed such that due to the elasticity of the material of the valve disc 7 the flaps 7 b displace the locating section 10 a to the right in fig3 when the syringe 14 is removed from the catheter hub 2 hereby the valve disc 7 is automatically closed as the position in fig2.