The initial studies of highly scattering biological materials by optical means were made by David Keilin and E.F. Hartree^1,2. Using the microspectroscope they observed that the cytochrome absorption bands from various microorganisms, which had been frozen in water or glycerol, were greatly enhanced by micro-recrystallization. Their samples were rapidly frozen in liquid nitrogen, and then rewarmed to a temperature at which a “red halo” was visible in the transmitted light. This produced a better definition of cytochrome absorption bands because of increased light scattering. Furthermore, Keilin showed that the low dispersion microspectroscope gave better visualization of cell and tissue absorption bands than did a higher resolution spectrograph.