Section 37. County commissioners may borrow money in anticipation of, and to be repaid from, the county tax of the current fiscal year. If said tax has been granted, such loans shall not exceed its amount; otherwise they shall not exceed the amount of the previous annual tax. They may issue therefor county notes maturing within one year after the date when the debt for which they are issued was incurred. Such notes, if issued for less than one year, may be renewed from time to time; provided, that the period from the date of the original loan to the date of maturity of any refunding loan shall not be more than one year. Notes issued hereunder may be sold at such discount as the commissioners may deem proper, the discount to be treated as interest paid in advance. Such notes shall be signed by the treasurer, countersigned by a majority of the commissioners, and shall expressly be made payable from the taxes of the current fiscal year, but shall nevertheless be negotiable. Except as otherwise expressly provided by law, neither county commissioners nor county treasurers, except in Suffolk and Nantucket counties, may borrow money or negotiate loans upon the credit of the county. Notes may also be issued between July first and July tenth, in accordance with this section, in anticipation of assessments payable to the county by cities, towns or corporations, under statutory provisions and unpaid at the end of the preceding fiscal year, in cases in which the total cost of the project for which the assessment is levied was paid by the county in the first instance.