The restricted energy loss of electrons, positrons, protons, and pions passing through nuclear emulsions has been measured by observation of the variation in blob and grain density as a function of $\gamma =\frac{1}{{(1-{\beta }^2)}^{\frac{1}{2}}}$. All measurements were made in small areas (7 ${\mathrm{cm}}^2$) of two Ilford $K-5\mathrm{}$ emulsion pellicles. A careful examination of the variation of blob density with track depth was made in both pellicles. The results of our measurements on the relativistic rise ($5<\mathrm{}\gamma <36\mathrm{}$) as well as on the Fermi plateau ($\gamma >100\mathrm{}$) are in agreement with the predictions of the Sternheimer formula using a mean ionization potential $I$ of 434 eV and a cutoff energy $W_0$ of 6-10 keV. An upper limit of 1% is placed on radiative corrections of the type predicted by Tsytovitch. Correction for the finite number of developable grains traversed by the primary produced a best fit with $W_0=6\mathrm{}$ keV, in excellent agreement with the maximum energy of a $\delta$ ray that comes to rest within the working volume of blob counting.

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