224 THE BACTERIOPHAGE AND ITS BEHAVIOR 



biology, not only from the point of view of bacteriophagy, but especially 

 in that it would show a possible origin of a natural immunity.* 



Bacterial metabohsm is also profoundly modified by the acquisition 

 of resistance, and as a rule the reestablishment of the original metabo- 

 lism coincides with the loss in resistance, but here also fixed mutations 

 may occur. 



It has already appeared from the preceding section that such 

 changes take place in mixed cultures, a condition due, as a matter of 

 fact, to resistant bacteria. 



Here again it is a case of repeating what has already been said with 

 regard to the agglutinability and the virulence of resistant bacteria. 

 Changes in the metabohsm can not be precisely described, for they vary 

 from one bacterium to another, even in a single culture of resistant 

 bacteria. From the beginning of my studies I have been interested in 

 ascertaining the fermentative characteristics of Shiga dysentery bacilli 

 resistant to the bacteriophage, but despite some hundreds of tests this 

 has been impossible, for every colony developing from seeding a mixed 

 culture on agar shows different fermentation reactions. 



Very recently Fejgin^^^ has described 3 different strains isolated from 

 a single mixed culture of Shiga bacilli. These three strains possessed 

 the following characters: 



Strain 1. The fermentation reactions were those of B. dysenteriae 

 Shiga. Inagglutinable with an anti-Shiga serum. The homologous 

 antiserum sgglutinated the Shiga bacillus, but not its own strain. 



Strain 2. Fermentation, with no gas production, takes place in 

 glucose, maltose and mannite. A Shiga antiserum agglutinates the 

 organism to a titre of 1 : 800, and this serum also agglutinates its homol- 

 ogous strain. 



Strain 3. With this strain fermentation, with gas formation, occurs 

 in lactose, glucose, maltose, arabinose, levulose, mannite, and dulcite. 

 It is agglutinated to a titre of 1 : 1600 by an anti-Shiga serum and by its 

 homologous serum. 



In brief, then, we have as mutations, first, an inagglutinable Shiga 

 bacillus, second, a Flexner bacillus, and third, a colon strain which does 



* For example, the Algerian sheep are refractory to spontaneous anthrax. 

 This, also, must be a fixed mutation produced through the effects of the para- 

 site, iS. anthracis. If all sheep could enjoy the same immunity we would say that 

 the sheep species is naturally refractory to anthrax and that we had here an 

 acquired immunity transformed into a natural immunity as the result of the 

 mutation. 



