  In this paper we solve the non-linear Lagrange's equations for the Nambu-Goto
closed bosonic string. We show that Ultradistributions of Exponential Type
(UET) are appropriate for the description in a consistent way string and string
field theories. We also prove that the string field is a linear superposition
of UET of compact support (CUET), and give the notion of anti-string. We
evaluate the propagator for the string field, and calculate the convolution of
two of them.
