A bag for a circuit of an installation for treatment of a biological liquid by chromatography, characterized in that it comprises: - a plurality of connectors (11A-11R) and a network for conveying liquid between said connectors (11 A-11 R), said conveying network being formed by a plurality of conduits (13A-13Q); and - two flexible films (65, 66) fastened to each other, said conduits (13A-13Q) being formed between the two said flexible films (65, 66); wherein a first conduit is provided with a first section (13J1), which has a first end (13J2) and a second end (13J3) which is an opposite end to the first end (13J1); wherein a second conduit is provided with a first section, which has a first end (13K2) and a second end (13K3) which is an opposite end to the first end (13K2), the first section (13J1) of the first conduit and the first section (13K1) of the second conduit being opposite; wherein a third conduit has a first end (13L1) and a second end (13L2) which is an opposite end to the first end (13L1), which third conduit is directly connected to said respective first ends (13J2, 13K2) of said respective first sections (13J1, 13K1) of said first conduit and said second conduit respectively by its first end (13L1) and its second end (13L2), without any intermediate section or component; wherein a fourth conduit has a first end (13M1) and a second end (13M2) which is an opposite end to the first end (13M1), which fourth conduit is directly connected to said respective second ends (13J3, 13K3) of said respective first sections (13J1, 13K1) of said first conduit and said second conduit respectively by its first end (13M1) and its second end (13M2), without any intermediate section or component; wherein a fifth conduit has a first end (13N1) and a second end (13N2) which is an opposite end to the first end (13N1), said fifth conduit being directly connected toboth the second end (13J3) of said first section (13J1) of said first conduit and said first end (13M1) of said fourth conduit by its first end (13N1), without any intermediate section or component, and said fifth conduit being directly connected to both said first end (13K2) of said first section (13K1) of said second conduit and said second end (13L2) of said third conduit by its second end (13N2), without any intermediate section or component; and said first conduit being directly connected to a chromatography column connector (11 L) by said first end (13J2) of its first section (13J1), and said second conduit being directly connected to a chromatography column connector (11 M) by said second end (13K3) of its first section (13K1); whereby the bag is configured such that the liquid to treat passes into said chromatography column via one of said first and second, conduits, exits via the other of said first and second conduits, and the liquid to treat may avoid said chromatography column by passing into said fifth conduit. - a plurality of connectors (11A-11R) and a network for conveying liquid between said connectors (11 A-11 R), said conveying network being formed by a plurality of conduits (13A-13Q); and - two flexible films (65, 66) fastened to each other, said conduits (13A-13Q) being formed between the two said flexible films (65, 66);