2 Variations in Bacteria Caused by Change of Medium 



draw certain conclusions regarding their probable causes. We hope 

 that at least the data here presented will be useful to future investi- 

 gators of this field. 



To produce a determinable change in either the properties or com- 

 position of bacteria, it is necessary to change their environment. This 

 is easily done by first altering the nature of the medium upon which 

 they are grown. By regulating the transplants with sufficient fre- 

 quency to make sure that the changes observed are not due to bac- 

 terial 'old age', and by continuing cultivation on the altered medium 

 long enough to produce a reasonably complete adaptation of the organ- 

 ism to its new environment, the experiments can be adequately con- 

 trolled, and an observable change of properties and composition, if 

 such is possible, can be obtained. 



The determination of the chemical composition of bacterial bodies 

 is not an easy task. Ordinary bacterial growths are actually composed 

 of very small quantities of material, and the production of sufficient 

 bacterial substance for a chemical analysis is difficult. 



PRELIMINARY PROCEDURE 



In order to determine the biological change in bacteria in any direc- 

 tion, it is necessary (i) to preserve the same organism throughout all 

 determinations, and (2) to determine the total activity of the organism 

 in statu quo as far as possible, and (3) lastly, to subject the organism to 

 constant varied conditions. 



In accordance with these requirements, a strain of B. Coli, which 

 showed ready and abundant growth, was selected and preserved 

 in all the following operations. It had been previously cultured on 

 meat-extract agar for an unknown number of generations, of which 

 at least 250 are known. In regard to this culture two questions 

 present themselves: Old Age and Adaptation. If the organism is 

 in a state of decrepitude, a transfer to other medium may mean only 

 rejuvenation, which could assert itself in the next generation on dif- 

 ferent medium on which the organism could have the widest scope 

 for metabolic processes. A tentative verification of this proceeded 

 as follows : A twenty-four hour culture of the organism was emulsified 

 in sterile salt solution of which a measured volume was plated on two 

 different media: meat-extract agar, and meat-infusion-dextrose 

 agar. After twenty-four hours' incubation the former showed 75 

 colonies, the latter showed 63. There seemed to be no distinguishing 



