Introduction:

Nuclear physics is currently making the transition from 
describing nuclei in terms of mesonic degrees of freedom 
(meson exchange/vector meson dominance) to describing them 
in terms of partonic degrees of freedom (quarks and gluons).
Facilities such as SLAC and CEBAF are now being used to 
study nuclear systems at energies up to 4-6 GeV.  Over the 
last few years a picture has been emerging:  mesonic degrees 
of freedom do not fully describe nuclear systems for large 
momentum transfers.  This is not to say that a perturbative 
QCD (pQCD) picture is correct at the energies currently 
available.  It seems reasonable to expect that pQCD should 
describe nuclear systems for very large momentum transfer 
due to the asymptotic freedom of the theory; however, the 
energies currently available place us in a region where both 
mesonic and partonic degrees of freedom can play a role.  
Despite the complications, it is an interesting and 
important area to investigate so that we might know better 
the limitations of both theories.

In this paper we plan to review recent experiments on 
deuteron photodisintegration performed at SLAC over the last 
few years and compare the predictions of a variety of models 
for these experiments. In the first section of the paper, we 
will review the experimental evidence for the existence of 
partons.  In the second, we will discuss the theoretical 
models of nuclear interactions such as meson-exchange models 
and the quark-gluon string model.  The third section will 
address the predictions of pQCD counting rules for cross 
sections and form factors at large momentum transfer.  In 
the fourth section, old and new experimental results will be 
presented and the performance of each of the models will be 
assessed.  In the final section, we will summarize what 
these experiments have taught us.