BACTERIA SUSCEPTIBLE TO BACTERIOPHAGY 255 



ordinary virus. On the other hand, it is conceivable that human infec- 

 tion might occur because of this enhanced virulence.* 



I have demonstrated the presence, very transitory however, of a 

 virulent bacteriophage for this organism in the blood of several white 

 rats which resisted a laboratory infection.^^i 



7. B. coli {Escherichia coli) 



Under normal conditions races of the bacteriophage virulent for 

 B. coli will be found in the intestinal tract of all animals (d'Herelle-^^^. 



B. coli normally occurs as a mixed culture in the intestine, always 

 possessing a resistance at the time of its isolation. It is necessary then, 

 after purification by colony isolation, to carry it through a series of sub- 

 cultures in order that it may lose this acquired resistance. 



On several occasions we have seen that bacteria undergo mutations 

 through the influence of the bacteriophage. Symbiosis with the 

 bacteriophage being a normal state for B. coli in the intestine, the 

 species of B. coli in its entirety is a mutant species. It is for this reason 

 that B. coli is the most heterogeneous of all bacterial species and that 

 each strain possesses its own peculiar characteristics as is shown, among 

 other things, by the serum reactions. 



After a series of subcultures and the loss of the acquired resistance! 



* As I have already stated'*" a really effective campaign against rats can not 

 be carried out by means of a bacterium. It is necessary to utilize an ultravirus 

 and that for the following reasons, which have been discussed in detail in the work 

 cited. Bacteria never cause an experimental contagious disease, even when the 

 natural disease attributed to this organism is fatal in the highest degree. Ex- 

 perimental cholera of fowls for example, is not contagious. On the contrary all 

 of the experimental diseases caused by ultra-viruses have the same degree of 

 contagiousness as the natural disease. A recently disclosed fact offers some sup- 

 port to my idea. Avian plague has been, up to the present time, unknown in 

 America. A bacteriologist there received from the Pasteur Institute in Paris 

 some of the plague virus and contaminated some chickens. The disease did not 

 remain localized to the infected farm-yard, but extended rapidly, and after a 

 few months it had actually become disseminated over several states. American 

 bacteriologists had an excellent opportunity to study the propagation of an 

 epizootic. They should have profited by this, for such an opportunity is en- 

 countered but rarely. 



But to return to the question of rats, an experiment would be easy to carry 

 out since Novy has succeeded in isolating an ultra-virus pathogenic for this 

 animal. 



t We know that at the time of isolation a mixed culture, either natural or 

 artificial, gives three kinds of colonies; mixed colonies, ultra-pure susceptible 

 colonies, and ultra-pure resistant colonies, the degree of resistance passing, ac- 



