Variations in Bacteria Caused by Change of Medium 15 



The fact that almost the same agglutination was observed in every 

 case shows by the most conclusive test we know that serologically the 

 organism retained the properties of the Colon bacillus. The organism 

 presents the most active antigenic properties when grown on a medium 

 containing fat, the least when grown without protein. The maximum 

 agglutination generally takes place when the antigenic and aggluti- 

 nated organisms are grown on the same medium. 



This establishes a very definite proof of the constitutional change 

 in the organism. The differences observed in agglutinability are 

 easily as great as those frequently utilized to demonstrate the existence 

 of different 'strains' of the same basic organism. 



Since antigenic differences appear to be produced so readily, it 

 seems to us reasonable to suppose that they can be found in all bac- 

 teria, and can be referred to the immediate past environment of the 

 organism; further real information they do not disclose. These 

 findings warn us, on the other hand, that bacteria are capable of change; 

 consequently, if the slightly variable strains, frequently kept for 

 investigation in laboratories, remain on the same medium for a long 

 period, they can be expected to lose their differential characteristics, 

 exhibiting only those that are common to all the strains. 



Connected with these fundamental changes we have sought evidence 

 of morphological alteration. The organism grown on Medium I 

 showed a bacillus about 2 micra long, in thickness I /4 its length ; 

 on Medium III, generally 3 to 5 micra long, almost I micron thick; 

 on Medium VII, 3 to 5 micra long, more than I micron thick. The 

 true significance of these morphological changes must be determined 

 by the variations already noted. 



GENERAL CONCLUSIONS 



We have shown that by changing the character of the media upon 

 which a given variety of bacteria is grown, the chemical constitution 

 of the bacteria can be made to vary and, with it, certain biological 

 characteristics such as agglutinability with immune serum and the 

 formation of sugar-splitting enzymes. In some instances the varia- 

 tions practically amount to the 'production' of a new strain. Accom- 

 panying morphological changes appear to be relatively unimportant. 



