IMMUNIZATION WITH BACTERIOPHAGE SUSPENSIONS 515 



tion of the healthy animal or in the one already sick, under the con- 

 ditions of the experiment, that is, in a contaminated area? Unques- 

 tionably it is the bacteriophage corpuscles themselves. The immediate 

 protection assured by the injection or even by the ingestion of the 

 bacteriophage suspension suffices to demonstrate this. An organic 

 immunity necessarily requires a certain time for its development. 

 Other phenomena of immunity, organic in nature, are produced only 

 after an incubation period, as the experiments on barbone will show. 



For the moment, let us conclude only that with sensitive animals 

 immunized by the injection of a suspension of the bacteriophage active 

 for the causative pathogenic bacterium, in a contaminated area, that 

 is to say, in an area where frequent reinfections may take place as a 

 result of the dissemination of the pathogenic bacteria in the external 

 environment, the principal role of protection is played by the bacterio- 

 phage itself. The other phenomena of immunity which may later 

 develop, stimulated by the other substances contained in the material 

 injected, play no role under such conditions unless it be a very second- 

 ary one. We will see that this proposition becomes reversed when 

 similar experiments are carried out in a non-contaminated area.^^^-^^i 



At the Institute of Parasitic and Infectious Diseases at Utrecht, 

 Kramer^^'* has carried out a series of experiments under conditions 

 comparable to those under which my work was done. And as this 

 question of the immunity conferred by the bacteriophage is of the 

 greatest importance from the point of view of our knowledge of "ex- 

 ogenous" immunity, I venture to insert in this text summaries of the 

 different experiments made by this author, since it may be that this 

 confirmation of my findings may prompt other investigators to follow 

 this method. 



In the first place, Kramer calls attention to the fact that, contrary 

 to what is reported by other authors, de Bheck was unable to obtain an 

 immunity against natural avian typhosis by injections, single or 

 repeated, of vaccines made of heated bacterial bodies, or even by em- 

 ploying "auto- vaccines." Incidentally, the experiments of Kramer 

 also show that a passive immunity is not conferred by the so-called 

 antibacterial sera. 



Without further discussion, let us consider Kramer's experiments 

 and the results which he obtained. The data presented below is 

 extracted from his protocols. 



Observation 1. Epizootic typhosis. 



Fifty of 100 pullets had died within a period of 8 days. Cultural 



