¹ From the Department of Biophysics, Cleveland Clinic Foundation, Cleveland.

1. The specific capacity of a suspension is that capacity which) combined in parallel with a certain resistance, electrically balances 1 cm. cube of the suspension.

2. The following formula holds for the specific capacity of a suspension of spheroids, each of which is composed of a well conducting interior surrounded by a thin membrane of a comparatively high resistance:

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C, specific capacity of suspension; C_o, static capacity of one sq. cm. of membrane; r, r₁ specific resistances respectively of suspension and of suspending liquid; 2 q major axis of spheroid, constant tabulated in Table I.

3. The following formula holds practically for any suspension whatever the form of the suspended particle.

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C = C₁₀₀ being the specific capacity of a suspension with a concentration of 100 per cent.

Formulæ (1a) and (1b) hold only for the case, when the frequency is so low, that the impedance of the static capacity of the membrane around a single particle is high as compared with the resistance of the interior of the particle. The formulae hold also for a suspension of homogeneous particles, when polarization takes place at the surface of each particle, provided the polarization resistance is low as compared with the impedance of the polarization capacity.

4. A description is given of a method for measuring the capacity of a suspension at frequencies between 800 and 4 million cycles. By means of a specially designed bridge, a substitution method is employed, by which in the last analysis the suspension is compared with the suspending liquid which is so diluted as to have the same specific resistance as the suspension, consecutive measurements being made in the same electrolytic cell.

5. Formula (1b) is verified by measurements of the capacity of suspensions of varying volume concentrations of the red corpuscles of a dog.

6. By means of the above measurements, the value of C_o is calculated by equation (1a).

7. It is found that C_o is independent of the frequency up to 4 million cycles and that it is also independent of the suspending liquid. These results furnish considerable evidence of the validity of the theory, that C_o represents the static capacity of a corpuscle membrane.

8. On this assumption and using a probable value for the dielectric constant of the membrane, the thickness of the membrane is calculated to be 3.3·10^–7 cm.

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