"SEC. 872. Sources of pension and retirement fund.—To this fund shall accrue all fines and forfeitures imposed by summary courts, all fines imposed upon commissioned officers under the authority of this chapter, and all sums accruing from vacancies in the authorized strength of officers and enlisted men, together with all other savings from positions the occupants whereof are or shall be entitled to the benefits of this chapter, and four per centum of the pay of every officer and enlisted man of the Constabulary, which shall be deducted from said pay monthly.
"All such sums accruing from fines, forfeitures, deductions, retentions, vacancies, and savings shall be noted and retained on the pay roll and deposited with the Insular Treasurer to the credit of the Constabulary pension and retirement fund."