Bag for storing a first substance injectable, in particular, in a human or animal body

A bag arrangement for intermixing two, separately stored substances, comprising a bag having a jacket defining an inner chamber for accommodating a first substance;

• and a piercing device having a chamber in which the jacket is received, a single piercing member provided on one side of the jacket, and a hollow abutment located opposite the piercing member on an opposite side of the jacket and forming a receptacle for accommodating a second substance, whereby upon actuation of the piercing device, the piercing member, piercing the opposite sides of the jacket, provides for intermixing of the first and second substances, wherein the piercing member has cutting ribs for cutting through the jacket.