(a) No relative of a patient in a state humane institution, nor the estate of such relative, shall be liable for any portion of the cost of support of any such patient in such institution for any period prior to July 1, 1955, except unpaid charges billed by the Welfare Commissioner.

(b) The provisions of sections 17a-502, 17b-222, 17b-223, 17b-228, 17b-232, 17b-745, 46b-215 and 53-304 shall not affect or impair the responsibility of any patient or patient’s estate for his care in a state humane institution prior to July 1, 1955, and the same may be enforced by any action by which such responsibility would have been enforceable prior to July 1, 1955, but only to the extent of that portion of such estate as is not needed for the support of the spouse, parents and dependent children of such patient.