  The concept of unified field theory is discussed. Two nonlinear field models
with world volume type action are considered, namely extremal space-time film
model and Born -- Infeld nonlinear electrodynamics. The natural appearance of
two long-range fundamental interactions, electromagnetism and gravitation, in
these field models is discussed. The quantum behaviour of the interacting
solitons-particles is considered. The concept of quasi-bounding quantization in
nonlinear field models is introduced.
