218 THE BACTERIOPHAGE AND ITS BEHAVIOR 



bacteria possessing an acquired resistance it is necessary to differentiate 

 the case where the resistance is active, that is to say, where it manifests 

 itself in the presence of a bacteriophage, from a latent resistance, a 

 resistance transmitted through inheritance in the absence of bacterio- 

 phage. We already know that a latent resistance is gradually lost. 



The acquisition of resistance by a bacterium is accompanied by 

 various biological modifications and these modifications are, indeed, 

 the more out-spoken as the degree of resistance is increased. The loss 

 of resistance is accompanied by a return to the usual form and to 

 normal properties. 



The most constant change shown by a bacterium in a state of active or 

 latent resistance is a loss in agglutinability with specific antisera 

 (d'Herelle^^^). The loss of agglutinability seems to be related to the 

 degree of acquired resistance, for the refractory state is accompanied by 

 a complete inagglutinability and there is only a diminution if the resist- 

 ance is partial. I have shown that such a loss or reduction in agglutin- 

 ability occurs with the following bacteria when they are refractory or 

 resistant: B. dysenteriae Shiga, Flexner, or Hiss, B. coli, B. kjphosus, 

 B. gallinarum and B. pestis. 



This loss in agglutinability correlative with the acquisition of resist- 

 ance has been shown by several others who have studied this question. 

 I might mention Gratia in particular'^ ^^ for he has tested the agglutin- 

 ability of different strains of B. coli presenting different degrees of 

 resistance.* 



I have shown that typhoid bacilli which are inagglutinable when 

 derived from the patient are also resistant to the action of the bacterio- 

 phage, which later attacks them when, after a series of passages 

 agglutinability is restored. ^^"^ 



The vitality of bacteria in a state of active resistance is a great deal 

 higher than that of normal bacteria. For example, the Shiga dysentery 

 bacillus has a relatively low vitality (there are few strains which may be 

 subcultured after a month; of the many cultures with which I have 

 worked none could be transplanted after two months on agar) but the 

 small, mucous, mixed colonies can be transplanted successfully after 

 18 months, the tube being sealed during the interval with a rubber 

 stopper. 



Bordet and Ciuca^ have shown that a resistant B. coli does not 

 produce the change in color of neutral red, that it is less readily phago- 

 cytized than the B. coli of the same normal strain and that its virulence 



* The table given by Gratia appears later in this section. 



