After all, paid-up shares are issued without any distinguishing numbers, so that the issue is an indivisible bulk of intangible fungibles, all share owners being co-owners of the bulk. If one of them purports to transfer 50 or declare a trust of 50, they are not dealing with 50 identifiable units of the bulk but with a fraction of the bulk corresponding to the proportion between the 50 and the total number of shares. It is convenient and natural to refer to numbers of shares rather than to fractions of share capital. The conversion of numbers into fractions creates the necessary certainty.