no SCIENCE REMAKING THE WORLD 



fully controlled, and checked by repetition. They 

 could not be further extended, however, without fresh 

 material from influenza cases and for some time it was 

 not possible to determine whether the blood of influenza 

 patients contained specific protective substances against 

 Bacterium pneumosintes, or whether protection might 

 be afforded by subcutaneous injections of the killed 

 organism a method of prevention that has proved so 

 efficacious against typhoid fever. An opportunity for 

 further study was finally provided by a recurrence of 

 epidemic influenza in New York City in January and 

 'February, 1922. 



With material obtained from a number of early cases 

 of influenza in this outbreak, all the essential steps in 

 the former investigation were repeated so that this 

 series of experiments served to check and confirm the 

 results of the earlier work. Especially significant was 

 the fact that the new and old strains reacted identically 

 in specific serum tests and that rabbits immunized 

 against the old strains were subsequently resistant to 

 the new ones, thus proving the identity of the micro- 

 organisms. 



With the 1922 strains of Bacterium pneumosintes the 

 experiments on the blood of recovered patients and on 

 the protection afforded by vaccination with killed cul- 

 tures could now be carried out. In the blood tests 

 specimens of serum were studied from nineteen persons 

 who had recovered from influenza from ten days to five 

 months previously, and from twenty-two other persons 

 who gave no history of influenza since 1920. The sera of 

 the twenty-two controls were uniformly negative in the 



