  We report on the search for a new spin-dependent P- and T-violating
interaction between nucleons mediated by light, pseudoscalar bosons such as the
axion which was invented to solve the strong CP problem. Our experimental
approach is to use an ultra-sensitive low-field magnetometer based on the
detection of free precession of co-located 3He and 129Xe nuclear spins using
SQUIDs as low-noise magnetic flux detectors. In the presence of an unpolarized
mass the precession frequency shif
