  An infinite number of perturbed k=0 Friedmann cosmologies filled with dust
and radiation is found. As we go up the sequence, the solutions contain an
increasing number of integration functions. With the coordinate gauge adopted
to co-move with the perturbed matter, the solution of a pair of coupled
equations for the trace h of the metric perturbations and for the radiation
density perturbations \delta\rho_r is the key to the problem. An estimate is
given of the temperature variation of the cosmic microwave background radiation
due to the Sachs-Wolfe effect. It is found that the temperature fluctuations
can grow faster than in the absence of radiation.
