The Electric Capacity of Suspensions of Red Corpuscles of a Dog

Measurements were made with a bridge, using a substitution method where-by the suspension is indirectly compared with a diluted serum which has the same specific resistance as the suspension. The bridge may be used with frequencies ranging from 800 to 4,500,000 cycles and its sensitivity is such that a capacity in parallel to 100 ohms can be measured with an accuracy of a few $\mu \mu \mathrm{f}$ at the lowest frequency. Measurements with a frequency of 87,000 cycles per sec. were made of suspensions of red corpuscles of a dog with volume concentrations between 10 and 88 percent, confirming the formula $C\left(\rho \right)=C_{100}(1-\frac{r_1}{r})$ previously ${\mathrm{derived}}^1$. By these measurements and the previous formula $C_0=\frac{C_{100}}{\mathrm{aq}}$ the capacity per ${\mathrm{cm}}^2$ of surface of a red corpuscle is calculated to be $.81\mu \mathrm{f}$. This capacity is independent of frequencies between 3600 and 4,500,000 cycles and is also independent of the suspending liquid. It is probably the static capacity of the membrane which surrounds the corpuscle. According to this assumption and using 3 for the dielectric constant, the thickness of the membrane is 3.3×${10}^{-7\mathrm{}}$ cm (monomolecular).