Studies on Cultural Requirements of Bacteria

It is a well-recognized fact that the nutritional requirements of an individual strain of any organism may be materially altered by prolonged cultivation on artificial media. Examples are so numerous and so well known that they need not be reviewed in detail. In many instances such changes are accompanied by alterations in the nature of the organism itself as in smooth to rough variation, while in other cases no such changes have been noted. The need of a particular organism for such an amino acid as tryptophane has been found to disappear after repeated subcultures on media with gradually diminishing concentrations of this amino acid (Fildes, Gladstone and Knight, 1933). The ability of organisms to grow on an exceedingly simple synthetic medium has been enhanced by the gradual substitution of such a solution for much more complex mixtures. Many other examples naturally suggest themselves. The diphtheria group has been widely studied in connection with its growth requirements, perhaps more so than other varieties of bacteria because of the interest attached to the process of toxin formation. It is now well known that great differences