206 THE BACTERIOPHAGE 



Sometimes death occurs more rapidly still, in certain cases in 

 a striking manner. Epizootics of avian typhosis have a high 

 mortality. In 1919 foci existed throughout the extent of France. 

 In general, the epizootic begins quickly; within the space of three 

 or four weeks a half, three-quarters, sometimes more, of the 

 fowls on a farm succumb. Then the disease assumes a sporadic 

 character, only an occasional animal dying during the course of a 

 year. The disease may disappear for a few months and then reap- 

 pear. The annual mortality amounts to forty to seventy per 

 cent of the population of the infected poultry-yards. Young 

 adults are the most susceptible, then the old animals; the chicks 

 are in general spared. 



Epizootics of typhosis extend rapidly over large areas; cer- 

 tain Departments were contaminated throughout in 1919. The 

 establishment of a new focus begins by the importation of the 

 organism from an infected region, either through the agency of a 

 flock of sheep or herd of cattle, or by horsemen (this last mode of 

 dissemination was particularly frequent during the war; this 

 explains the extension of the disease during the years 1917 and 

 1918). The disease rages for a few days on a farm, passes to a 

 neighboring farm, and then extends rapidly into the surrounding 

 villages. 



The pathogenic bacillus remains alive and virulent during 

 several months in the regions where the infection has been epi- 

 demic. In several tests it has been shown that an isolated in- 

 fected chicken-yard, cleaned and left unoccupied for six to eight 

 months, still contains virulent germs, for, when repopulated with 

 chickens from a region free of the disease, the infection breaks 

 out again within a few days among the new occupants. 



Avian typhosis being a disease in general but little known, I 

 have thought it useful to consider it in some detail, since it will 

 allow us the better to understand the facts now to be presented. 



The role of the bacteriophage in the course of the disease 



Because of the exceptional severity of the infection in avian 

 typhosis it has been possible to follow only four cases which re- 

 covered. In all, the picture has been identical. In the morn- 

 ing the infected chicken remains on the ground, " balled up," 



