This historical note is mainly based on a relatively unknown paper published by Albert Einstein in Revista de la Universidad Nacional de Tucumán in 1941. Taking the ideas of this work as a leitmotiv, we review the discussions about the particle problem in the theory of gravitation within the historical context by means of the study of seminal works on the subject. The revision shows how the digressions regarding the structure of matter and the concise problem of finding regular solutions of the pure field equations turned out to be intrinsically unified in the beginning of the programme towards a final theory of fields. The mentioned paper (Einstein 1941a) represents the basis of the one written by the same author in collaboration with Wolfgang Pauli in 1943, in which, following analogous lines, the proof of the non-existence of regular particle-type solutions was generalized to the case of cilyndrical geometries in Kaluza-Klein theory (Einstein & Pauli, 1943). Besides, other generalizations were subsequently presented. The (non)-existence of such solutions in classical unified field theory was undoubtedly an important criterion leading Einstein’s investigations. This aspect was gathered with expertness by Jeroen van Dongen in a recent work, though restricting the scope to the particular case of the investigations on Kaluza-Klein theory (van Dongen, 2002). Here, we discuss the particle problem within a more general context, presenting in this way a complement to Dongen’s study.