The judge of probate may appoint the register of probate, a deputy probate register, or clerk of his court as register of the juvenile division of the probate court. Such register of the juvenile division shall prepare all petitions for investigation, summons, writs and other necessary papers, and shall perform such duties as required by the judge of probate, and he shall exercise and be competent to do all acts required of the judge of probate, except judicial acts. Such register so appointed shall receive for his services under this chapter, in addition to his regular salary, such sum as the board of supervisors shall fix: Provided, however, That in counties having a population of 100,000, and not more than 350,000 inhabitants, according to the last federal census, the compensation shall be not less than $500.00 annually.