Abstract: The present invention relates to a device for introducing a liquid other than blood in a blood vessel, composed of a hollow needle having a front end and an axially opposite rear end, a hollow female support base which is fixed to the rear end of the needle or which is connected to the rear end thereof by a supple, transparent tube, and of a membrane which is disposed transversely with respect to said support base, which membrane is at the same time permeable to air, impermeable to blood and permeable to the liquid to be injected.