"Those polymerizates in which the monomers used are of type (i) in which R3, R4, and R5 are methyl groups, Z is an NH group, and A(???) is a halide, methoxysulfate, or ethoxysulfate ion, are very particularly preferred; acrylamidopropyltrimethylammonium chloride is a particularly preferred monomer (i)." . . . .