{ diff(x1, t) = 1*k10*(k1*k2 - x1*(k3 + k4))/k10,
  diff(x2, t) = 1*k10*(x1*k3 - x2*(k6 + k9) - k5*x2^2)/k10,
  diff(x3, t) = 1*k10*(x2*k6 - x3*(k7 + k8))/k10 }