Fick’s law [Adolf E. Fick, German physiologist, 1829–1901] , 1. (in chemistry and physics) an observed law stating that the rate at which one substance diffuses through another is directly proportional to the concentration gradient of the diffusing substance. 2. (in medicine) an observed law stating that the rate of diffusion across a membrane is directly proportional to the concentration gradient of the substance on the two sides of the membrane and inversely related to the thickness of the membrane.
