242 THE BACTERIOPHAGE 



The immunization experiments by means of cultures of the 

 bacteriophage have been conducted in two different ways: 



a. In an epizootic area of avian typhosis, where there would 

 be an immunization against natural infection; and 



b. In a non-infected area, as in barbone, where the results 

 could be checked against experimental controls. These last 

 experiments have shown clearly the exact conditions under which 

 immunization by means of the bacteriophage can be carried out. 



IMMUNIZATION AGAINST AVIAN TYPHOSIS 



Further mention need not be made of the immunization ex- 

 periments conducted in the laboratory, which have been dis- 

 cussed in the chapter dealing with the phenomena observed in 

 the course of epizootics of avian typhosis. 



Immunization experiments in a region where the epizootic 

 was present, as in the case of avian typhosis, presented an especial 

 difficulty, or rather, a complication. It has been mentioned 

 that aside from the typical typhosis, due to B. gallinarum^ there 

 are several varieties of paratyphoses, each caused by a particu- 

 lar species of bacterium. The differences which these bacterial 

 species present from the biochemical and agglutinative points 

 of view and which serve to differentiate them are of no particu- 

 lar significance from the point of view of this study. In so far 

 as the action of the bacteriophage is concerned, for each of these, 

 a strain of bacteriophage having an extreme virulence (+ + + +) 

 for B. gallinarum possesses the same activity for all the French 

 and American strains as well as for B. jeffersonii. The activity 

 is less pronounced for B. pullorum A, still less for B. pullorum B, 

 and is lacking for B. pfaffi and for B. rettgerei. With such a 

 strain of bacteriophage the reactions are: B. gallinarum + + ++, 

 B. jeffersonii + + ++, B. pullorum A ++, B. pullorum B +, 

 B. pfaffi 0, and B. rettgerei 0. Inversely, a strain of bacteriophage 

 secured from fowls resistant to paratyphosis due to B. pfaffi 

 (focus at Trainel, Aube) had the following virulences: B. galli- 

 narum 0, B. jeffersonii 0, B. pullorum A 0, B. pullorum B +, 

 B. pfaffi + + + + , and B. rettgerei 0. 



The immunization experiments thus become singularly com- 

 plicated, particularly since both typhosis and the paratyphoses 





