It shall be the duty of the master to exercise reasonable care to provide for his servant a reasonably safe place in which to work, reasonably safe appliances and instrumentalities for his work and fit and competent persons as his colaborers and to exercise reasonable care in the appointment or designation of a vice-principal and to appoint as such vice-principal a fit and competent person. The default of a vice-principal in the performance of any duty imposed by law on the master shall be the default of the master.