The physical properties of cytoplasm. A study by means of the magnetic particle method. Part II. Theoretical treatment

Abstract 1. 1. The paper gives the theory of the magnetic particle method, in which some of the mechanical properties of a fluid are estimated by observing the movements of magnetic particles in it due to applied fields. 2. 2. For the very small particles likely to be used in biological systems the inertia can be neglected. 3. 3. The effect of scale is derived for particles of irregular shape in a newtonian liquid. 4. 4. Exact formulae are quoted, for the three cases most often encountered, for an ovary ellipsoid of revolution in an infinite newtonian liquid. References to the general ellipsoid are given. 5. 5. The effects of the irregular shape of a particle, of boundaries, and of non-newtonian and elastic behaviour of the fluid are discussed qualitatively. 6. 6. Some theoretical notes are given on producing large gradients of magnetic field. 7. 7. Some comparative numerical values of the stresses in certain biological applications are evaluated.