Section 142. Sections one hundred and thirty-eight to one hundred and forty-one, inclusive, shall not apply to Perkins School for the Blind, or to any organization incorporated under the laws of the commonwealth prior to January first, nineteen hundred and thirty-eight, and theretofore engaged in work for the blind; nor shall the provision of said sections restrict any blind person in the pursuit of a gainful occupation if he does not hold out his blindness as an inducement of patronage, or prohibit the featuring of blind artists at duly licensed places of amusements, or at entertainments for the benefit of charitable, benevolent or religious organizations not subject to said sections.