History: P.A. 73-279 prohibited discrimination based on physical disability including blindness and qualified that prohibition by adding unless it is shown ... that such disability prevents performance of the work involved; P.A. 78-148 prohibited discrimination on basis of mental retardation; P.A. 79-631 replaced Sec. 4-61b with Sec. 4-61c in Subsec. (c); P.A. 80-422 substituted nondiscriminato