  The damped Lyman alpha systems seen in the spectra of high redshift QSOs
offer the means to determine element abundances in galaxies observed while
still at an early stage of evolution. Such measurements, which have only
recently come within reach, complement and extend the data provided by studies
of different stellar populations in our Galaxy and of extragalactic H~II
regions which have up to now formed the basis of galactic chemical evolution
models. In this paper we demonstrate the potential of this new approach with
high-resolution echelle observations of several elements in the z(abs) =
2.27936 absorption system in the bright z(em) = 2.940 QSO 2348-147. The
absorbing galaxy appears to be chemically unevolved, with heavy element
abundances only 1/100 of solar; if it is the progenitor of a spiral galaxy like
our own, it is unlikely to have collapsed to form a thin disk by z = 2.3
(corresponding to a look-back time of approximately 13 Gyr for H_0 = 50
km/s/Mpc and q_0 = 0.01). Our data allow us to measure the nitrogen-to-oxygen
ratio at a metallicity lower than those of the most metal-poor dwarf galaxies
known. We find that, relative to the solar scale, N is more underabundant than
O by at least a factor of 15. This result is broadly in line with current ideas
on the relative importance of primary and secondary production of N; future
measurements in several damped Lyman alpha systems will permit more stringent
tests of models for the evolution of the N/O ratio with time. Oxygen and other
alpha-elements are overabundant relative to Fe by no more than the factor of
about 3 typical of metal-poor stars in the disk and halo of the Milky Way.
