RESISTANCE OF BACTERIA 213 



It is interesting to see what happens when one seeds symbiotic cul- 

 tures into a suspension of susceptible bacteria or into pure suspensions 

 of virulent corpuscles. Wlien dealing with a mixed culture of co- 

 existent bacteria of low resistance and corpuscles of low virulence the 

 implantation of the mixed culture into a suspension of susceptible 

 bacteria has no effect; the result is a mixed culture of the same nature. 

 If, on the contrary, one inoculates a suspension of the bacteriophage into 

 such a mixed culture everything depends' upon the degree of virulence. 

 If the virulence of the corpuscles is very high or is maximum bacterio- 

 phagy takes place; when the virulence is not high nothing is changed. 



In the case of mixed cultures where very virulent corpuscles and 

 very resistant bacteria co-exist things take place differently. 



When a mixed, agglutinated culture is inoculated into a pure culture 

 of the bacteriophage, that is, into a suspension previously inoculated 

 and which has undergone complete dissolution, the growth consists of an 

 agglutinated culture, just as though the inoculation had been made into 

 fresh sterile bouillon. 



If some of the agglutinate, even if washed, is introduced into a sus- 



the bacteriophage and they are refractory to bacteriophagy. This is precisely 

 contrary to the statements of Arkwright. These occasional, naturally con- 

 taminated strains are, however, easy to purify. Ultrapure colonies from them 

 give in subculture ultrapure cultures indefinitely, presenting upon agar but a 

 single type of colony. After a number of transplantings, when the resistance 

 to bacteriophagy has disappeared these ultrapure colonies show all of the charac- 

 ters of normal strains and all of the colonies on agar are susceptible to bac- 

 teriophagy. 



In this same contribution Arkwright says that I have classified the Shiga 

 dysentery bacilli as a homogeneous species as regards bacteriophagy but that my 

 experiments contradict this statement for I have found strains which, when de- 

 rived from the body, were refractory to bacteriophagy. Manifestly this author 

 has not comprehended the difference between natural resistance and acquired 

 resistance. After a few passages in ultrapure culture the strains which were not 

 attacked at the time of their recovery from the body because of a resistance 

 acquired in the body become susceptible and subject to attack. As a matter of 

 fact, such a resistant state is extremely rare insofar as the dysentery bacillus is 

 concerned. But even if it occurred very frequently it would have nothing to 

 do with the question of homogeneity. A species is homogeneous with reference 

 to the bacteriophage when all of the strains presenting the characters of the 

 species are subject to attack by any race whatever of a bacteriophage which is 

 virulent for any strain whatever of this species. The only refractory strains of 

 such a species are those which possess an acquired resistance, and this is lost by a 

 series of transfers in ultrapure culture. They then undergo bacteriophagy in 

 exactly the same manner as a susceptible strain. 



