Section 3
SEC. 3. In case the tax prescribed herein is not fully paid at the time specified herein, such tax shall be increased by twenty-five per centum, the increment to be part of the tax and the entire amount shall be payable upon demand or the period specified therein: Provided, That any failure to pay upon demand or within the period specified therein, such tax plus surcharge shall be subject to interest at fourteen per centum per annum computed from the date the demand has been duly served or received or such specified date until the actual payment is made.