For an apparatus for the extra-corporal treatment of blood wherein blood is supplied from a body to a vacuum bottle via a conduit, an insertion spike for piercing a closure plug of a vacuum bottle has a front end with a pointed tip and includes a first passage extending from the front end to a connecting piece for connection to a gas supply means, the front end having a perforated side wall for the diffused discharge of gases admitted through the first passage and a second passage having means for connection to a blood conduit and extending to an opening in the side of the insertion spike adjacent the perforated side wall.