Indeed, let us denote with formula_1 the spatially non-uniform concentration of the chemo-attractant and with formula_2 its gradient. Then the chemotactic cellular flow (also called current) formula_3 that is generated by the chemotaxis is linked to the above gradient by the law: formula_4, where formula_5 is the spatial density of the cells and formula_6 is the so-called ’Chemotactic coefficient’. However, note that in many cases formula_6 is not constant: It is, instead, a decreasing function of the concentration of the chemo-attractant formula_8: formula_9.