Pursuant to the recognized obligations of governments to guarantee the social security of their employees and in order to provide for the retirement on an annuity, or otherwise, of all persons being paid salaries in whole or in part from grants of Federal funds to the several States, Puerto Rico, the Virgin Islands, and Guam pursuant to the terms of the Act approved July 2, 1862, for the endowment and support of colleges of agriculture and mechanic arts [7 U.S.C. 301 et seq.], and Acts supplementary thereto providing for instruction in agriculture and mechanic arts, for the establishment of agricultural experiment stations, and for cooperative extension work in agriculture and home economics, all States, Puerto Rico, the Virgin Islands, and Guam are after March 4, 1940, authorized, notwithstanding any contrary provisions in said Acts, to withhold from expenditure, from Federal funds advanced under the terms of said Acts, amounts designated as employer contributions to be made by the States, Puerto Rico, the Virgin Islands, or Guam to retirement systems established in accordance with the laws of such States, Puerto Rico, the Virgin Islands, or Guam, or established by the governing boards of colleges of agriculture and mechanic arts in accordance with the authority vested in them, and to deposit such amounts to the credit of such retirement systems for subsequent disbursement in accordance with the terms of the retirement systems in effect in the respective States, Puerto Rico, the Virgin Islands, and Guam: Provided, That there shall not be deducted from Federal funds and deposited to the credit of retirement accounts as employer contributions, amounts in excess of 5 per centum of that portion of the salaries of employees paid from such Federal funds: Provided further, That, for the purpose of making deposits and contributions in retirement systems in favor of any employee, in no event shall the deductions from any Federal fund advanced pursuant to the foregoing Acts be in greater proportion to the total deductions for such employee than the salary received under such Federal funds bears to the total salary from Federal sources: Provided further, That the deposits and contributions from funds of Federal origin to any retirement system established by a State, Puerto Rico, the Virgin Islands, or Guam or a land-grant college must be at least equaled by the total contributions thereto on the part of the individuals concerned, the State, Puerto Rico, the Virgin Islands, or Guam, and the counties: And provided further, That no deductions for the foregoing purposes shall be made from Federal funds in support of employees appointed pursuant to the terms of the foregoing Acts, whose salaries are paid wholly by the States, Puerto Rico, the Virgin Islands, or Guam: Provided further, That the provisions of this section shall not apply to any employee paid in whole or in part from Federal funds who may be subject to subchapter III of chapter 83 of title 5.