The Particle Problem in Classical Gravity: A historical note on 1941
  This note is based on a relatively unknown paper of Albert Einstein published in 1941 in the Revista de la Universidad Nacional de Tucuman. That work can be regarded as the prequel of the one written in 1943 in collaboration with Wolfgang Pauli, where, along the same lines, a proof of the non-existence of certain non-singular solutions in Kaluza-Klein theory was given. More generally, disproving the existence of regular solutions in classical unified field theories became, specially after 1930, an important criterion leading Einstein's investigations on unified field theory. This is the context in which Einstein's paper of 1941 and its generalizations of 1943 and 1948 become important. 
Mariano Galvagno, Gaston Giribet