55. For the purposes of this chapter, the actual cost, to a taxpayer, at a given time after 1971, of shares owned by him of any class of the capital stock of a corporation resulting from an amalgamation on 31 December 1971 and thereafter without interruption until that time and which were acquired by him on account of the amalgamation at the time of conversion of shares owned by him in the capital stock of a corporation replaced, is the proportion of the actual cost, for him, of all his shares so converted, represented by the ratio between the fair market value, immediately after the amalgamation, of the shares of that class so acquired by him and that at the same time of all shares of the capital stock of the new corporation that he has so acquired.