THE BACTERIOPHAGE AND THE BACTERIUM 79 



Transplants into bouillon continue to give mixed cultures, cloudy, 

 with less marked but definite changes in appearance. These alterations in 

 appearance are separated by intervals of only a few hours. 



This same experiment is performed with another strain of anti-dysen- 

 tery bacteriophage, the inoculation being made from a colony on a 

 secondary culture two months old. After three days there is uniform 

 turbidity. In five days the medium is almost limpid. After eleven days 

 it is very cloudy and after eighteen days it is clear with a slight sediment. 

 All subcultures remain sterile and the medium contains a very active 

 bacteriophage. 



In the mixed cultures with changing appearance the struggle 

 between the bacteriophage and the bacterium inclines first in 

 favor of one contending force and then to the advantage of the 

 other. The final issue is at times in favor of the bacteriophage, 

 at times in favor of the bacterium, and the number of transfers 

 necessary to bring about a final issue is extremely variable. 



In vitro, the struggle generally ends with the bacterium the 

 victor. In Part II of this text we will see that in vivo, with mixed 

 cultures showing fluctuations, the issue of the struggle is deter- 

 mined in some measure by the superior organism (that is, the 

 animal body) in which the contending forces are operating. 



Bacteriophage of very high virulence 



With a bacteriophage of very high virulence secondary cultures 

 are relatively rare, and when they appear they offer a very charac- 

 teristic aspect, at least in so far as B. dysenteriae is concerned. 

 The medium remains perfectly limpid, the bacterial culture ap- 

 pears agglutinated, multiplying slowly in the bottom of the tube 

 or deposited on the walls. These agglutinated masses may attain 

 a size as large as the head of a pin and they can not be dissociated 

 by shaking. With other bacteria the agglutination is less marked. 



Subcultures from these agglutinated mixed cultures give, 

 indefinitely it appears, mixed cultures always presenting the same 

 appearance. 2 



2 As one of the consequences, very important from the practical 

 point of view, we will see that numerous so-called pure bacterial cultures 

 are to be found in most laboratories which are in reality mixed cultures, 

 contaminated from the time of their origin with a bacteriophage. 



