The experiments described in this paper are part of a larger number which we have been carrying out for the past 2 years. Although they have not entirely fulfilled their purpose, which was to explain the so called "mutation," "dissociation," "Umwandlung," "transformation" process, they have served to formulate a helpful working hypothesis.
Certain difficulties inherent in this kind of study must be recognized. One is that colony formation is a property associated with growth on solid media and any procedure involving the use of fluid media introduces a change which is relatively uncontrolled. Another is that mucoid and rough colony forms are not the only variant types encountered; at best, they may be considered as being the most frequent. Finally, it is apparent to us that the findings reported in this paper with respect to enteritidis organisms do not correspond with those of other species of organisms, especially of the respiratory group which we have studied (1, b). Possibly, however, they apply generally to the typhoid, paratyphoid-enteritidis species.
To summarize, it may be stated that the transformation process in the mouse typhoid enteritidis group is an easily reversible one, controlled in part, at least, by three factors, any of which may conceivably operate under natural conditions: (1) temperature, which, influences the appearance of mucoid forms; (2) fluidity of culture media, which tends to favor rough variants; and (3) bacteriophage, which stimulates the appearance of both variants. Since by manipulating these factors the transformation process may be incited at will in either direction, it is probably not genetic in nature.