Spectral Fourier analysis of experimentally acquired velocity time dependencies, <i>V(t)</i>, of shuttle endoplasmic motility in an isolated strand of plasmodium of slime mold <i>Physarum</i> <i>Polycephalum</i> has been realized. <i>V(t)</i> registration was performed in normal conditions and after the treatment by respiration inhibitors, which lead to a complete cessation of endoplasmic motion in the strand. Spectral analysis of the velocity time dependences of the endoplasm allows obtaining two distinct harmonic components in the spectra. Their ratio appeared to be constant in all cases, ν2/ν1=1.97±0.17. After the inhibitors are washed out respiratory system becomes normal, gradually restoring the activity of both harmonic oscillatory sources with time. Simulated velocity time dependences correspond to experimental data with good accuracy.