The Chief of Engineers may authorize the employment of physicians under agreement, to make such physical examinations of employees or prospective employees as he may consider essential, on a fee or regular employment basis, and all agreements entered into prior to , for such purposes are validated, and the Comptroller General is authorized and directed to allow credit in the accounts of disbursing officers for reasonable payments made prior to , for such services.March 2, 19451945-03-02March 2, 19451945-03-02