  Two hypothesized solutions of the mass discrepancy problem are cold dark
matter (CDM) and modified Newtonian dynamics (MOND). The virtues and vices of
these very different hypotheses are largely disjoint, making the process of
distinguishing between them very dependent on how we weigh disparate lines of
evidence. One clear difference is the nature of the principal mass constituent
of the universe (CDM or baryons). This difference in the baryon fraction ($f_b
\approx 0.1$ vs. 1) should leave a distinctive signature in the spectrum of
fluctuations in the cosmic microwave background. Here I discuss some of the
signatures which should be detectable in the near future. The most promising
appears to be the ratio of the amplitudes of the first two peaks relative to
the intervening trough.
