J. BRONFENBRENNER 549 



tain number of bacteria fail to undergo lysis and continue to multiply, in spite of 

 the presence of a high concentration of the lytic agent in the medium. This more or 

 less profuse secondary growth consists of bacteria resistant to the action of bacterio- 

 phage. Such secondary cultures ordinarily lose their resistance to phage in a 

 short time, if they are transferred repeatedly to new media, to eliminate all 

 traces of phage by dilution, or if they are grown in media to which has been added 

 some specific serum, to eliminate the phage by neutralization.' Often this loss of 

 resistance takes place slowly, and in its early stages may remain unobserved, unless 

 special effort is made to bring it to light.^ Occasionally this property of resisting the 

 action of bacteriophage may be retained by secondary cultures through very long 

 periods of cultivation in the absence of phage.^ 



According to the conception of D'Herelle, appearance of resistant individuals in 

 the susceptible culture is the result of specific adaptation of individual bacteria to 

 the environment. Some cultures, according to him, may exhibit a "natural resist- 

 ance" to certain races of bacteriophage (although they may be lysed by others). ^ 

 Other cultures, on the contrary, may be so highly susceptible that all the bacteria 

 are killed by the bacteriophage before they are able to develop any resistance.^ 

 Ordinarily, many bacteria in a susceptible culture resist the invasion and "may thus 

 acquire an immunity to the bacteriophage corpuscles which attack them." The phe- 

 nomena of immunity in bacteria against phage are "strictly comparable with those 

 observed in higher animals."'' According to Asheshov, this development of resistance 

 is subject to fluctuations entirely analogous to those observed in epidemics among 

 higher animals.^ When conditions are suitable, a certain number of bacteria "recover" 

 from infection by directly destroying the bacteriophage corpuscles present within 

 their protoplasm,^ or by secreting substances which inhibit the activity of bacterio- 

 phage.* 



Apart from the fact that the very possibiUty of the development of active im- 

 munity by the bacteria has been doubted by many, the circumstance that bacteria 

 resistant to one strain of phage may be susceptible to lysis by another homologous 



' Saldanha, A.: loc. cit.; T^iava, G., and Pozerski, E.: Compt. rend. Soc. dc hiol., 84, 708. 1921; 

 Brcinl, F., and Hoder, F.: Ccnlralbl. f. BaklcrioL, Orig., 96, i. 1925; Bronfenbrenner, J., and Korb, 

 C: Proc. Soc. Expcr. Biol. &= Med., 23, 3. 1925; Bronfenbrenner, J., Muckenfuss, R., and Korb, C: 

 J. Expcr. Med., 44, 607. 1926; Bordet, J., and Ciuca, M.: Compl. rend. Soc. dc hiol., 84, 748. 1921. 



' Failure to recognize this partial return to susceptibility is undoubtedly responsible for the er- 

 roneous conclusions of several investigators who believe that the concentration of bacteriophage in 

 the solution may increase at the expense of resistant bacteria (Meissner, G.: loc. cit.; Zdansky, E.: 

 Ztschr.f. Hyg. u. Injektionskrankh., 103, 164. 1924; Lepper, E. H.: Brit. J. Exper. Path., 4, 53. 1923). 



3 Bronfenbrenner, J., Muckenfuss, R., and Korb, C.: loc. cit.; Bordet, J., and Ciuca, M.: loc. cit. 



"•d'Herelle, F.: Immunity in'Natural Infectious Disease, p. 259. 1924. 



5 Asheshov, I. N.: Compt. rend. Soc. dc bioL, 93, 644. 1925; d'Herelle, F.: The Bacteriophage 

 and Its Behavior, pp. 1S2-83. 1926. 



* Asheshov, I. N.: Compt. rend. Soc. de hiol., 93, 1329. 1925. 

 'd'Herelle, F. : The Bacteriophage and Its Behavior, p. 239. 1926. 



* Grumbach, A., and Dimtza, A.: loc. cit.; d'Herelle, F.: The Bacteriophage and Its Behavior, 

 p. 240. 1926. 



