{ diff(x1, t) = (1*k1*k2 + (-1)*k1*k3*x1 + (-1)*k1*k7*x1*x5/(k6 + x13))/k1,
  diff(x2, t) = (1*k1*k4 + (-1)*k1*k5*x2 + (-1)*k1*(k8*x2*x5 + k9*x2*x15))/k1,
  diff(x3, t) = (1*k1*k7*x1*x5/(k6 + x13) + (-1)*k1*k10*x3)/k1,
  diff(x4, t) = (1*k1*(k8*x2*x5 + k9*x2*x15) + (-1)*k1*k11*x4)/k1,
  diff(x5, t) = (1*k1*(k15*x16 + k16*x8)/((k12 + x6)*(k13 + k52)*(k14 + x19)) + (-1)*k1*k32*x5)/k1,
  diff(x6, t) = (1*k1*k18*x4/(k17 + x5) + (-1)*k1*k33*x6)/k1,
  diff(x7, t) = (1*k1*k19*x2 + (-1)*k1*k34*x7)/k1,
  diff(x8, t) = (1*k1*(k20*x12 + k21*x14) + (-1)*k1*k35*x8)/k1,
  diff(x9, t) = 0,
  diff(x10, t) = 0,
  diff(x11, t) = (1*k1*k28*x3 + (-1)*k1*k40*x11)/k1,
  diff(x12, t) = (1*k1*k30/(k29 + x11) + (-1)*k1*k41*x12)/k1,
  diff(x13, t) = (1*k1*k31*x4 + (-1)*k1*k42*x13)/k1,
  diff(x14, t) = ((-1)*k1*k43*x14 + 1*k1*k44*x3)/k1,
  diff(x15, t) = (1*k1*(k24*x3 + k25*x4)/(k23 + x6) + (-1)*k1*k37*x15)/k1,
  diff(x16, t) = (1*k1*k26*x3 + (-1)*k1*k38*x16)/k1,
  diff(x17, t) = (1*k1*k45*x13 + (-1)*k1*k46*x17)/k1,
  diff(x18, t) = (1*k1*k49*x3 + (-1)*k1*k51*x18)/k1,
  diff(x19, t) = (1*k1*k48*x17/(k47 + x18) + (-1)*k1*k50*x19)/k1 }