462 THE BACTERIOPHAGE AND ITS BEHAVIOR 



We find then, in typhoid fever, — an intestinal infection complicated 

 by a septicemia — the same facts as seen in bacillary dysentery. 



The virulence of the bacteriophage isolated from the stools of the 

 typhoid patient is not limited, in general, to a single pathogenic bacillus; 

 at one and the same time it extends, in some degree, to some or all of 

 the bacilli of the colon-typhoid-dysentery group. This fact is partic- 

 ularly noted in mild cases or those of average severity. In the severe 

 cases the bactericidal action is more specific and is often limited to the 

 specific pathogenic organism and to B. coli, the latter always being at- 

 tacked. In certain very severe cases the specificity becomes such that 

 up to the beginning of actual improvement only the bacUlus isolated 

 from the patient is attacked, whether it has been secured by stool or 

 by blood culture, to the exclusion of other baciUi, taken either from old 

 laboratory cultures or from strains recently isolated from other patients. 

 It seems, then, that in the course of their struggle each of the two 

 organisms present, — bacteriophage and bacterium^ — acquires an indi- 

 vidual personality, which differentiates them from other organisms 

 of the same species rendered banal as a result of cultivation. 



In addition to 28 non-fatal cases which were studied in order to deter- 

 mine the influence of the bacteriophage on the course of the disease, 

 three fatal cases were observed. In these three cases, at no period of the 

 disease could the presence of a bacteriophage be demonstrated active 

 for B. typhosus, either for a stock strain or for the baciUus from the 

 patient. Furthermore, examination of the strains from the intestinal 

 contents from five individuals who had died of typhoid fever failed to 

 show any activity for the typhoid bacillus. But the bacteriophage was 

 not entirely absent, since in six of these eight cases a bacteriophage of 

 moderate activity for the colon bacillus was found. This bacteriophage 

 did not, however, show any activity for the pathogenic organisms. 

 Death in typhoid fever results, usually, because of a failure of the bac- 

 teriophage to adapt itself to the bacteriophagy of the invading baciUus. 



May death occur because of the acquisition of a resistant condition 

 by the typhoid bacillus, which protects it from the action of the bac- 

 teriophage, as we have seen in the case of dysentery? There has been 

 no opportunity to establish this up to the present but it is the more 

 probable, since, in vitro as in vivo, the tendency toward resistance is 

 certainly more marked in the typhoid bacillus than for B. dysenteriae. 

 In any case, this cause of death is certainly the exception, even in 

 typhoid. It must necessarily accompany a septicemia when it occurs. 



In typhoid, as in dysentery, the investigation of the virulence of the 



