{ diff(x1, t) = (1*k14*(k1*x2 + k3*x1*x3/(k4 + x3) + k5) + (-1)*k14*k2*x1)/k14,
  diff(x2, t) = (1*k14*k6*x2*(1 - k7*x2) + (-1)*k14*k8*x1*x2/(k9 + x2))/k14,
  diff(x3, t) = (1*k14*(k10*x1*x2/(k11 + x2) + k13) + (-1)*k14*k12*x3)/k14 }