++++ Social security for migrant workers - Invalidity insurance - Person in receipt of benefits residing in a Member State other than the competent State - Medical examinations - Requirement that the recipient travel to the territory of the competent Member State at the request of the institution responsible for payment - Conditions - Journey not harmful to the health of recipient and expenses paid - Unfitness to travel certified by the institution of the place of stay - Verification on the spot of unfitness to travel by the institution responsible for payment - Permissibility (Council Regulation No 574/72, Article 51(1) )