On chemical reactors that can count

It is known that spatially distributed excitable systems can transmit and process information if one relates the logical "true" state with a high concentration of a selected reagent and the logical "false" state with a low concentration of the same reagent. The information coded in the propagating pulses of concentration can be processed in properly arranged reactors. In this paper, we show how to build a reactor counting the number of pulses that arrive at a given point of space or that propagate within a signal channel. We discuss two types of such reactors. The first consists of many memory cells, and each of the arriving pulses excites a subsequent cell. The second gives the number of arriving pulses in the binary positional representation. All basic elements of these chemical counters have been tested experimentally using a photosensitive Ru-catalyzed Belousov-Zhabotinsky reaction.