The ideas in this paper were developed further in a second part [Mathisson, 1942], which was edited by P A M Dirac after Mathisson's death, who wrote in a footnote to the introduction:
Ang mga ideya sa papel na ito ay binuo ng karagdagang sa ikalawang bahagi ng [Mathisson, 1942], na kung saan ay edited by PAM Dirac matapos Mathisson ng kamatayan, na nag-wrote sa isang footnote sa pagpapakilala: