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Optical and magneto-optical data from the perovskite itinerant ferromagnet ${\mathrm{SrRuO}}_{3}$ are presented and compared to fully relativistic, local spin-density approximation band-structure calculations. We find that the basic features of the optical data are well described by the ferromagnetic band calculation. To test recent predictions that the ferromagnetic transition in ${\mathrm{}\mathrm{SrRuO}}_{3}$ is driven by long-wavelength longitudinal spin fluctuations, we track the temperature dependence of the $\mathrm{O}(2p)\ensuremath{\rightarrow}\mathrm{Ru}(4d)$ interband transition which we observe in the magneto-optic conductivity. The absence of significant changes in the energy of this transition suggests that the ferromagnetic order is destroyed largely through transverse, not longitudinal, fluctuations of the ferromagnetic moment. We discuss the implications of these observations for the electronic structure of the ruthenium perovskites.