We consider a onedimensional array of coupled stirred tank reactors. Each reactor operates with the bistable chlorite-iodide reaction. The reaction admits two stable steady states (A and B). At time zero, all reactors are at steady state A except the first reactor which is at steady state B. Provided the coupling (exchange rate) between each reactor is sufficiently large, a propagating wave joining A to B is initiated. We determine the speed of the front and show that it fails to propagate if the exchange rate is below a nonzero value. In addition, we investigate the time history of the front and identify three distinct stages. First, we note a small time regime dominated by a diffusion mechanism; second, we note a front propagating with almost constant speed; third, we note a boundary layer regime corresponding to the end of the front and the approach to the final uniform steady state. We explain all three stages by analyzing a simple model.

An intensified photodiode array forms the heart of a sensitive spectrophotofluorometry system that permits the rapid and non‐invasive determination of fluorescence emission spectra in the skin of living, non‐anesthetized animals. Using this system, we found it possible to obtain good emission and excitation spectra of the material responsible for the weak red fluorescence that characterizes normal mouse skin, and to follow the biosynthesis and subsequent clearance of protoporphyrin IX in the skin of non‐anesthetized mice that had been given various doses of the porphyrin precursor 5‐aminolevulinic acid.

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The absorbance and fluorescence spectra of Hematoporphyrin IX, Photofrin, and Photofrin II are measured as a function of pH, concentration, and temperature, in order to isolate the ionic equilibria from the monomer/dimer/aggregate equilibria. Based on photometric and volumetric titrations, the distribution diagram for four ionic species is presented, with pKa, values of 2.7, 5.2, and 9.1. Protonation sites for these pKa's are assigned.