The electrical conductivity of human tissue at low frequencies is discussed when a uniform electric field is applied to some tissue containing many cells. Human tissue is described as a suspension of particles in a conducting solution. Relations are derived for the apparent conductivity of a cell surrounded by a membrane. These relations can be used to estimate the accuracy of a model that considers the cell as a non-conducting particle. Usually, a tissue is composed of several types of particles. A relationship that expresses the effective conductivity of a suspension of one type of ellipsoidal particles could be found in the literature. The orientation of the particles could be uniform or they could be randomly distributed. For non-conducting particles, this expression is known as Archie's law. The expression is extended such that also the effective conductivity of a suspension of various types of particles can be calculated. The result is evaluated for the cortex of the brain using experimental data given in the literature.