Apparatus for Maintaining Bacterial Cultures in the Steady State

When cultures of bacteria are transferred in the usual way, both the character of the cells, and the composition of the medium are constantly changing. If the cell concentration is held constant, on the other hand, the composition of the medium (including enzymes and viruses) in which the growth occurs, must also be constant and any change in the concentration of any substance indicates a change in the organism. This condition of a steady state is therefore the simplest to study, from a theoretical point of view. A number of devices for the maintenance of cultures in continuouslog growth have been described (Felton and Dougherty (1924); Novick and Szilard (1950); Anderson (1953); Myers and Clark (1944); Bryson (1952)). The present apparatus involves no new principles, but may be assembled from commercially available units. The flow of culture media is controlled by a photoelectric cell which is exposed to a light beam passing through the culture.