THE BACTERIOPHAGE IN DISEASE 209 



month fifty-one of the ninety-eight fowls died; then the epizootic 

 disappeared. In May, 1918 it reappeared in less violent form. 

 Twenty-five of one hundred and four fowls died in the period 

 from May to September, and it again disappeared. In 1919 it 

 broke out again early in April. On the 21st of May, twenty-one 

 of eighty had died. At this time I began my observations. 



On May 21, specimens of the excrement of thirty of the fifty- 

 nine survivors were taken. Examination, made later in the lab- 

 oratory, showed in twenty-six a bacteriophage of weak or moder- 

 ate activity for B. gallinarum (23 were +, 3 were ++), in four 

 it was absent. On May 22, two chickens contracted the disease. 

 The strains taken the day before were numbered and examination 

 showed that an active bacteriophage had not been found in these 

 two animals. On May 23 one of the two chickens affected the 

 day before died. On May 24, a third chicken, sick in the morning, 

 died in the following night. Its excrement, collected on May 22, 

 did not contain a bacteriophage active for B. gallinarum. On 

 the morning of May 24 the chicken which had been taken sick 

 on May 22 and which had resisted showed in its intestinal con- 

 tents a bacteriophage of extreme activity (+ + ++) toward the 

 pathogenic bacillus. On May 26 the fourth chicken, one of those 

 whose feces had not showed an active bacteriophage when examined 

 on May 22, was affected. It resisted, and on May 28 its symptoms 

 had disappeared. The disease disappeared suddenly and during 

 the next three months no new cases developed. 



On May 30 the feces of thirty chickens were examined and the 

 following results were obtained: 



Virulence for B. gallinarum; in five + + ++, in twenty-one 

 + + +, in four + + . 



We see, then, on May 22, four animals among thirty in which 

 the intestinal bacteriophage lacked activity for the pathogenic 

 bacillus. These four animals contracted the disease during 

 the four following days. In the twenty-six specimens collected 

 on May 22 and showing positive results, the bacteriophage showed 

 a relatively weak virulence. Nine days later this activity was 

 very much greater, that is, at the time when the epizootic ceased. 

 What, then, took place in this interval? The bird which became 

 sick on May 22 and which resisted showed in its feces, when ex- 



