Adolf Fick

Russ Hobbie and I discuss Fick’s laws of diffusion in Chapter 4 of the 4th edition of Intermediate Physics for Medicine and Biology. The German scientist Adolf Fick (1829–1901) was a classic example of a researcher who was comfortable in both physics and physiology. He enrolled at the University of Marburg with the goal of studying mathematics and physics, but eventually switched to medicine, and earned an MD in 1852. Of particular interest to me is that he wrote a classic textbook titled Medical Physics (1856), which was one of the first books on this topic. I have not read this book, which almost certainly is written in German (although I am half German through my father’s side, I cannot speak or read the language). Nevertheless, I wonder if Intermediate Physics for Medicine and Biology might be a descendant of this text.

Fick was only 26 when he proposed his two laws of diffusion. The first law (Eq. 4.18a in our book)—similar to Ohm’s law for electrical current or Fourier’s law for heat conduction—states that the diffusive flux is proportional to the concentration gradient. The constant of proportionality is the diffusion constant, which Fick first introduced. Fick’s second law (Eq. 4.24) arises by combining his first law with the equation of continuity (Eq. 4.2) and is what we generally refer to as the diffusion equation. He tested his two laws by measuring the diffusion of salt in water. He even noticed the strong temperature dependence of the diffusion constant.

Fick contributed to physiology and medicine in several ways. He made the first successful contact lens, and he developed a method to measure cardiac output based on oxygen consumption and blood oxygen concentration. You can find more information about his life at http://www.corrosion-doctors.org/Biographies/FickBio.htm.